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 $176.95   11.612%   $197.4974   $197.50   $197.50   $197.50  
  Purchase #2 $54.25   8.603%   $58.9171   $58.92   $58.90   $58.90  
  Purchase #3 $247.75   10.735%   $274.346   $274.35   $274.35   $274.30  
  Purchase #4 $222.91   4.239%   $232.3592   $232.36   $232.35   $232.40  
  Purchase #5 $125.44   10.263%   $138.3139   $138.31   $138.30   $138.30  
  Purchase #6 $175.85   13.589%   $199.7463   $199.75   $199.75   $199.70  
  Purchase #7 $28.71   12.110%   $32.1868   $32.19   $32.20   $32.20  
  7 purchase totals = $1,031.86       $1,133.3667   $1,133.38   $1,133.35   $1,133.30