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 $53.92   8.119%   $58.2978   $58.30   $58.30   $58.30  
  Purchase #2 $243.38   12.760%   $274.4353   $274.44   $274.45   $274.40  
  Purchase #3 $118.46   9.596%   $129.8274   $129.83   $129.85   $129.80  
  Purchase #4 $250.25   10.272%   $275.9557   $275.96   $275.95   $276.00  
  Purchase #5 $136.67   10.626%   $151.1926   $151.19   $151.20   $151.20  
  Purchase #6 $109.52   12.381%   $123.0797   $123.08   $123.10   $123.10  
  Purchase #7 $45.68   5.362%   $48.1294   $48.13   $48.15   $48.10  
  7 purchase totals = $957.88       $1,060.9179   $1,060.93   $1,061.00   $1,060.90