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 $176.29   11.192%   $196.0204   $196.02   $196.00   $196.00  
  Purchase #2 $153.93   9.809%   $169.029   $169.03   $169.05   $169.00  
  Purchase #3 $144.95   10.470%   $160.1263   $160.13   $160.15   $160.10  
  Purchase #4 $63.86   9.107%   $69.6757   $69.68   $69.70   $69.70  
  Purchase #5 $62.71   3.592%   $64.9625   $64.96   $64.95   $65.00  
  Purchase #6 $115.33   8.186%   $124.7709   $124.77   $124.75   $124.80  
  Purchase #7 $184.51   12.413%   $207.4132   $207.41   $207.40   $207.40  
  7 purchase totals = $901.58       $991.9980   $992.00   $992.00   $992.00