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 $88.68   12.235%   $99.53   $99.53   $99.55   $99.50  
  Purchase #2 $182.99   11.295%   $203.6587   $203.66   $203.65   $203.70  
  Purchase #3 $56.63   13.102%   $64.0497   $64.05   $64.05   $64.00  
  Purchase #4 $6.82   13.564%   $7.7451   $7.75   $7.75   $7.70  
  Purchase #5 $20.79   10.220%   $22.9147   $22.91   $22.90   $22.90  
  Purchase #6 $122.80   4.161%   $127.9097   $127.91   $127.90   $127.90  
  Purchase #7 $209.28   13.520%   $237.5747   $237.57   $237.55   $237.60  
  7 purchase totals = $687.99       $763.3826   $763.38   $763.35   $763.30