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 $168.98   9.282%   $184.6647   $184.66   $184.65   $184.70  
  Purchase #2 $170.46   13.489%   $193.4533   $193.45   $193.45   $193.50  
  Purchase #3 $39.31   13.820%   $44.7426   $44.74   $44.75   $44.70  
  Purchase #4 $92.64   10.829%   $102.672   $102.67   $102.65   $102.70  
  Purchase #5 $247.83   3.524%   $256.5635   $256.56   $256.55   $256.60  
  Purchase #6 $176.60   13.141%   $199.807   $199.81   $199.80   $199.80  
  Purchase #7 $9.42   11.608%   $10.5135   $10.51   $10.50   $10.50  
  7 purchase totals = $905.24       $992.4166   $992.40   $992.35   $992.50