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 $49.77   10.174%   $54.8336   $54.83   $54.85   $54.80  
  Purchase #2 $173.42   12.602%   $195.2744   $195.27   $195.25   $195.30  
  Purchase #3 $236.34   6.788%   $252.3828   $252.38   $252.40   $252.40  
  Purchase #4 $118.72   5.264%   $124.9694   $124.97   $124.95   $125.00  
  Purchase #5 $212.42   9.840%   $233.3221   $233.32   $233.30   $233.30  
  Purchase #6 $216.84   12.494%   $243.932   $243.93   $243.95   $243.90  
  Purchase #7 $220.86   3.828%   $229.3145   $229.31   $229.30   $229.30  
  7 purchase totals = $1,228.37       $1,334.0288   $1,334.01   $1,334.00   $1,334.00