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 $244.63   11.837%   $273.5869   $273.59   $273.60   $273.60  
  Purchase #2 $108.31   4.450%   $113.1298   $113.13   $113.15   $113.10  
  Purchase #3 $169.48   6.670%   $180.7843   $180.78   $180.80   $180.80  
  Purchase #4 $77.99   8.690%   $84.7673   $84.77   $84.75   $84.80  
  Purchase #5 $152.81   6.107%   $162.1421   $162.14   $162.15   $162.10  
  Purchase #6 $71.35   4.452%   $74.5265   $74.53   $74.55   $74.50  
  Purchase #7 $147.45   6.412%   $156.9045   $156.90   $156.90   $156.90  
  7 purchase totals = $972.02       $1,045.8414   $1,045.84   $1,045.90   $1,045.80