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 $65.42   12.122%   $73.3502   $73.35   $73.35   $73.40  
  Purchase #2 $89.52   5.748%   $94.6656   $94.67   $94.65   $94.70  
  Purchase #3 $189.88   11.536%   $211.7846   $211.78   $211.80   $211.80  
  Purchase #4 $83.44   12.567%   $93.9259   $93.93   $93.95   $93.90  
  Purchase #5 $42.80   12.714%   $48.2416   $48.24   $48.25   $48.20  
  Purchase #6 $141.80   11.201%   $157.683   $157.68   $157.70   $157.70  
  Purchase #7 $237.30   4.314%   $247.5371   $247.54   $247.55   $247.50  
  7 purchase totals = $850.16       $927.1880   $927.19   $927.25   $927.20