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 $65.61   5.826%   $69.4324   $69.43   $69.45   $69.40  
  Purchase #2 $190.84   13.597%   $216.7885   $216.79   $216.80   $216.80  
  Purchase #3 $137.52   6.822%   $146.9016   $146.90   $146.90   $146.90  
  Purchase #4 $221.71   4.441%   $231.5561   $231.56   $231.55   $231.60  
  Purchase #5 $8.66   8.331%   $9.3815   $9.38   $9.40   $9.40  
  Purchase #6 $243.99   12.367%   $274.1642   $274.16   $274.15   $274.20  
  Purchase #7 $45.73   6.548%   $48.7244   $48.72   $48.70   $48.70  
  7 purchase totals = $914.06       $996.9487   $996.94   $996.95   $997.00