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 $209.38   11.501%   $233.4608   $233.46   $233.45   $233.50  
  Purchase #2 $39.99   6.769%   $42.6969   $42.70   $42.70   $42.70  
  Purchase #3 $163.26   7.518%   $175.5339   $175.53   $175.55   $175.50  
  Purchase #4 $174.96   6.678%   $186.6438   $186.64   $186.65   $186.60  
  Purchase #5 $205.32   5.413%   $216.434   $216.43   $216.45   $216.40  
  Purchase #6 $48.90   8.115%   $52.8682   $52.87   $52.85   $52.90  
  Purchase #7 $15.99   10.345%   $17.6442   $17.64   $17.65   $17.60  
  7 purchase totals = $857.80       $925.2818   $925.27   $925.30   $925.20