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 $44.85   13.138%   $50.7424   $50.74   $50.75   $50.70  
  Purchase #2 $174.86   4.791%   $183.2375   $183.24   $183.25   $183.20  
  Purchase #3 $122.80   8.375%   $133.0845   $133.08   $133.10   $133.10  
  Purchase #4 $67.93   6.682%   $72.4691   $72.47   $72.45   $72.50  
  Purchase #5 $184.62   12.301%   $207.3301   $207.33   $207.35   $207.30  
  Purchase #6 $189.72   6.298%   $201.6686   $201.67   $201.65   $201.70  
  Purchase #7 $123.84   7.289%   $132.8667   $132.87   $132.85   $132.90  
  7 purchase totals = $908.62       $981.3989   $981.40   $981.40   $981.40