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 $57.92   8.217%   $62.6793   $62.68   $62.70   $62.70  
  Purchase #2 $96.72   4.760%   $101.3239   $101.32   $101.30   $101.30  
  Purchase #3 $220.29   7.820%   $237.5167   $237.52   $237.50   $237.50  
  Purchase #4 $246.99   10.661%   $273.3216   $273.32   $273.30   $273.30  
  Purchase #5 $124.91   8.703%   $135.7809   $135.78   $135.80   $135.80  
  Purchase #6 $175.63   8.419%   $190.4163   $190.42   $190.40   $190.40  
  Purchase #7 $246.89   6.664%   $263.3427   $263.34   $263.35   $263.30  
  7 purchase totals = $1,169.35       $1,264.3814   $1,264.38   $1,264.35   $1,264.30