Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $245.33   11.540%   $273.6411   $273.64   $273.65   $273.60  
  Purchase #2 $150.28   8.147%   $162.5233   $162.52   $162.50   $162.50  
  Purchase #3 $129.48   10.826%   $143.4975   $143.50   $143.50   $143.50  
  Purchase #4 $177.84   8.471%   $192.9048   $192.90   $192.90   $192.90  
  Purchase #5 $163.26   11.133%   $181.4357   $181.44   $181.45   $181.40  
  Purchase #6 $247.66   8.415%   $268.5006   $268.50   $268.50   $268.50  
  Purchase #7 $192.78   6.225%   $204.7806   $204.78   $204.80   $204.80  
  7 purchase totals = $1,306.63       $1,427.2836   $1,427.28   $1,427.30   $1,427.20