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 $215.71   10.150%   $237.6046   $237.60   $237.60   $237.60  
  Purchase #2 $171.27   13.507%   $194.4034   $194.40   $194.40   $194.40  
  Purchase #3 $63.46   4.290%   $66.1824   $66.18   $66.20   $66.20  
  Purchase #4 $113.97   7.649%   $122.6876   $122.69   $122.70   $122.70  
  Purchase #5 $81.30   6.140%   $86.2918   $86.29   $86.30   $86.30  
  Purchase #6 $141.69   10.867%   $157.0875   $157.09   $157.10   $157.10  
  Purchase #7 $123.93   8.156%   $134.0377   $134.04   $134.05   $134.00  
  7 purchase totals = $911.33       $998.2950   $998.29   $998.35   $998.30