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 $70.99   8.124%   $76.7572   $76.76   $76.75   $76.80  
  Purchase #2 $97.75   8.725%   $106.2787   $106.28   $106.30   $106.30  
  Purchase #3 $99.40   8.491%   $107.8401   $107.84   $107.85   $107.80  
  Purchase #4 $206.52   10.234%   $227.6553   $227.66   $227.65   $227.70  
  Purchase #5 $83.43   11.201%   $92.775   $92.78   $92.80   $92.80  
  Purchase #6 $203.36   13.109%   $230.0185   $230.02   $230.00   $230.00  
  Purchase #7 $189.78   11.683%   $211.952   $211.95   $211.95   $212.00  
  7 purchase totals = $951.23       $1,053.2768   $1,053.29   $1,053.30   $1,053.40