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 $232.82   11.862%   $260.4371   $260.44   $260.45   $260.40  
  Purchase #2 $91.53   6.699%   $97.6616   $97.66   $97.65   $97.70  
  Purchase #3 $196.73   10.571%   $217.5263   $217.53   $217.55   $217.50  
  Purchase #4 $36.49   12.405%   $41.0166   $41.02   $41.00   $41.00  
  Purchase #5 $33.60   10.191%   $37.0242   $37.02   $37.00   $37.00  
  Purchase #6 $94.95   7.792%   $102.3485   $102.35   $102.35   $102.30  
  Purchase #7 $225.95   13.532%   $256.5256   $256.53   $256.55   $256.50  
  7 purchase totals = $912.07       $1,012.5399   $1,012.55   $1,012.55   $1,012.40