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 $65.39   9.268%   $71.4503   $71.45   $71.45   $71.50  
  Purchase #2 $130.39   12.328%   $146.4645   $146.46   $146.45   $146.50  
  Purchase #3 $108.55   9.587%   $118.9567   $118.96   $118.95   $119.00  
  Purchase #4 $79.61   9.291%   $87.0066   $87.01   $87.00   $87.00  
  Purchase #5 $184.47   6.666%   $196.7668   $196.77   $196.75   $196.80  
  Purchase #6 $61.44   12.323%   $69.0113   $69.01   $69.00   $69.00  
  Purchase #7 $206.79   8.624%   $224.6236   $224.62   $224.60   $224.60  
  7 purchase totals = $836.64       $914.2798   $914.28   $914.20   $914.40