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 $181.75   7.779%   $195.8883   $195.89   $195.90   $195.90  
  Purchase #2 $91.45   8.657%   $99.3668   $99.37   $99.35   $99.40  
  Purchase #3 $170.54   6.293%   $181.2721   $181.27   $181.25   $181.30  
  Purchase #4 $62.43   7.331%   $67.0067   $67.01   $67.00   $67.00  
  Purchase #5 $193.73   9.863%   $212.8376   $212.84   $212.85   $212.80  
  Purchase #6 $98.76   9.757%   $108.396   $108.40   $108.40   $108.40  
  Purchase #7 $150.91   5.312%   $158.9263   $158.93   $158.95   $158.90  
  7 purchase totals = $949.57       $1,023.6938   $1,023.71   $1,023.70   $1,023.70