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 $233.67   8.483%   $253.4922   $253.49   $253.50   $253.50  
  Purchase #2 $124.50   11.809%   $139.2022   $139.20   $139.20   $139.20  
  Purchase #3 $7.40   8.120%   $8.0009   $8.00   $8.00   $8.00  
  Purchase #4 $58.38   12.125%   $65.4586   $65.46   $65.45   $65.50  
  Purchase #5 $152.75   6.387%   $162.5061   $162.51   $162.50   $162.50  
  Purchase #6 $232.41   8.376%   $251.8767   $251.88   $251.90   $251.90  
  Purchase #7 $22.56   7.554%   $24.2642   $24.26   $24.25   $24.30  
  7 purchase totals = $831.67       $904.8009   $904.80   $904.80   $904.90