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 $206.93   4.856%   $216.9785   $216.98   $217.00   $217.00  
  Purchase #2 $36.77   9.445%   $40.2429   $40.24   $40.25   $40.20  
  Purchase #3 $244.54   8.315%   $264.8735   $264.87   $264.85   $264.90  
  Purchase #4 $55.68   13.865%   $63.4   $63.40   $63.40   $63.40  
  Purchase #5 $201.55   11.741%   $225.214   $225.21   $225.20   $225.20  
  Purchase #6 $121.98   13.394%   $138.318   $138.32   $138.30   $138.30  
  Purchase #7 $171.90   7.811%   $185.3271   $185.33   $185.35   $185.30  
  7 purchase totals = $1,039.35       $1,134.3540   $1,134.35   $1,134.35   $1,134.30