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 $163.70   8.528%   $177.6603   $177.66   $177.65   $177.70  
  Purchase #2 $68.60   8.846%   $74.6684   $74.67   $74.65   $74.70  
  Purchase #3 $120.77   8.345%   $130.8483   $130.85   $130.85   $130.80  
  Purchase #4 $153.42   3.230%   $158.3755   $158.38   $158.40   $158.40  
  Purchase #5 $119.30   12.352%   $134.0359   $134.04   $134.05   $134.00  
  Purchase #6 $214.30   4.754%   $224.4878   $224.49   $224.50   $224.50  
  Purchase #7 $135.93   3.766%   $141.0491   $141.05   $141.05   $141.00  
  7 purchase totals = $976.02       $1,041.1253   $1,041.14   $1,041.15   $1,041.10