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 $55.91   12.635%   $62.9742   $62.97   $62.95   $63.00  
  Purchase #2 $25.60   7.344%   $27.4801   $27.48   $27.50   $27.50  
  Purchase #3 $52.40   3.395%   $54.179   $54.18   $54.20   $54.20  
  Purchase #4 $77.52   9.584%   $84.9495   $84.95   $84.95   $84.90  
  Purchase #5 $224.44   12.123%   $251.6489   $251.65   $251.65   $251.60  
  Purchase #6 $161.80   8.122%   $174.9414   $174.94   $174.95   $174.90  
  Purchase #7 $243.31   11.871%   $272.1933   $272.19   $272.20   $272.20  
  7 purchase totals = $840.98       $928.3664   $928.36   $928.40   $928.30