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 $204.52   13.351%   $231.8255   $231.83   $231.85   $231.80  
  Purchase #2 $230.71   6.584%   $245.8999   $245.90   $245.90   $245.90  
  Purchase #3 $250.40   12.451%   $281.5773   $281.58   $281.60   $281.60  
  Purchase #4 $148.44   13.687%   $168.757   $168.76   $168.75   $168.80  
  Purchase #5 $62.71   13.219%   $70.9996   $71.00   $71.00   $71.00  
  Purchase #6 $141.59   5.372%   $149.1962   $149.20   $149.20   $149.20  
  Purchase #7 $15.91   13.323%   $18.0297   $18.03   $18.05   $18.00  
  7 purchase totals = $1,054.28       $1,166.2852   $1,166.30   $1,166.35   $1,166.30