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 $16.96   11.833%   $18.9669   $18.97   $18.95   $19.00  
  Purchase #2 $237.79   6.843%   $254.062   $254.06   $254.05   $254.10  
  Purchase #3 $27.93   13.593%   $31.7265   $31.73   $31.75   $31.70  
  Purchase #4 $197.49   5.869%   $209.0807   $209.08   $209.10   $209.10  
  Purchase #5 $233.76   9.360%   $255.6399   $255.64   $255.65   $255.60  
  Purchase #6 $164.95   8.328%   $178.687   $178.69   $178.70   $178.70  
  Purchase #7 $82.62   3.220%   $85.2804   $85.28   $85.30   $85.30  
  7 purchase totals = $961.50       $1,033.4434   $1,033.45   $1,033.50   $1,033.50