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 $241.67   11.174%   $268.6742   $268.67   $268.65   $268.70  
  Purchase #2 $87.28   11.164%   $97.0239   $97.02   $97.00   $97.00  
  Purchase #3 $39.52   12.817%   $44.5853   $44.59   $44.60   $44.60  
  Purchase #4 $48.84   12.680%   $55.0329   $55.03   $55.05   $55.00  
  Purchase #5 $25.53   5.452%   $26.9219   $26.92   $26.90   $26.90  
  Purchase #6 $29.36   3.284%   $30.3242   $30.32   $30.30   $30.30  
  Purchase #7 $238.67   3.466%   $246.9423   $246.94   $246.95   $246.90  
  7 purchase totals = $710.87       $769.5047   $769.49   $769.45   $769.40