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 $68.69   3.151%   $70.8544   $70.85   $70.85   $70.90  
  Purchase #2 $236.25   8.467%   $256.2533   $256.25   $256.25   $256.30  
  Purchase #3 $212.32   4.788%   $222.4859   $222.49   $222.50   $222.50  
  Purchase #4 $149.77   7.347%   $160.7736   $160.77   $160.75   $160.80  
  Purchase #5 $5.53   7.616%   $5.9512   $5.95   $5.95   $6.00  
  Purchase #6 $230.59   7.475%   $247.8266   $247.83   $247.85   $247.80  
  Purchase #7 $230.58   6.324%   $245.1619   $245.16   $245.15   $245.20  
  7 purchase totals = $1,133.73       $1,209.3069   $1,209.30   $1,209.30   $1,209.50