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 $55.43   6.358%   $58.9542   $58.95   $58.95   $59.00  
  Purchase #2 $210.70   12.269%   $236.5508   $236.55   $236.55   $236.60  
  Purchase #3 $209.27   6.727%   $223.3476   $223.35   $223.35   $223.30  
  Purchase #4 $197.50   5.128%   $207.6278   $207.63   $207.65   $207.60  
  Purchase #5 $151.44   5.622%   $159.954   $159.95   $159.95   $160.00  
  Purchase #6 $186.81   8.851%   $203.3446   $203.34   $203.35   $203.30  
  Purchase #7 $45.66   3.414%   $47.2188   $47.22   $47.20   $47.20  
  7 purchase totals = $1,056.81       $1,136.9978   $1,136.99   $1,137.00   $1,137.00