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 $197.69   13.779%   $224.9297   $224.93   $224.95   $224.90  
  Purchase #2 $183.89   12.129%   $206.194   $206.19   $206.20   $206.20  
  Purchase #3 $83.83   13.180%   $94.8788   $94.88   $94.90   $94.90  
  Purchase #4 $90.55   13.663%   $102.9218   $102.92   $102.90   $102.90  
  Purchase #5 $13.70   10.372%   $15.121   $15.12   $15.10   $15.10  
  Purchase #6 $104.54   5.561%   $110.3535   $110.35   $110.35   $110.40  
  Purchase #7 $227.69   6.218%   $241.8478   $241.85   $241.85   $241.80  
  7 purchase totals = $901.89       $996.2466   $996.24   $996.25   $996.20