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 $67.93   11.444%   $75.7039   $75.70   $75.70   $75.70  
  Purchase #2 $221.43   5.324%   $233.2189   $233.22   $233.20   $233.20  
  Purchase #3 $176.95   6.621%   $188.6659   $188.67   $188.65   $188.70  
  Purchase #4 $29.75   11.713%   $33.2346   $33.23   $33.25   $33.20  
  Purchase #5 $245.51   5.527%   $259.0793   $259.08   $259.10   $259.10  
  Purchase #6 $8.69   12.779%   $9.8005   $9.80   $9.80   $9.80  
  Purchase #7 $129.86   5.342%   $136.7971   $136.80   $136.80   $136.80  
  7 purchase totals = $880.12       $936.5002   $936.50   $936.50   $936.50