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 $59.40   10.725%   $65.7707   $65.77   $65.75   $65.80  
  Purchase #2 $225.63   12.336%   $253.4637   $253.46   $253.45   $253.50  
  Purchase #3 $204.80   3.188%   $211.329   $211.33   $211.35   $211.30  
  Purchase #4 $28.64   3.593%   $29.669   $29.67   $29.65   $29.70  
  Purchase #5 $130.31   12.708%   $146.8698   $146.87   $146.85   $146.90  
  Purchase #6 $162.74   3.218%   $167.977   $167.98   $168.00   $168.00  
  Purchase #7 $50.65   3.635%   $52.4911   $52.49   $52.50   $52.50  
  7 purchase totals = $862.17       $927.5703   $927.57   $927.55   $927.70