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 $107.71   10.440%   $118.9549   $118.95   $118.95   $119.00  
  Purchase #2 $168.32   12.676%   $189.6562   $189.66   $189.65   $189.70  
  Purchase #3 $131.31   9.667%   $144.0037   $144.00   $144.00   $144.00  
  Purchase #4 $72.91   11.392%   $81.2159   $81.22   $81.20   $81.20  
  Purchase #5 $59.39   8.653%   $64.529   $64.53   $64.55   $64.50  
  Purchase #6 $245.49   8.849%   $267.2134   $267.21   $267.20   $267.20  
  Purchase #7 $244.86   6.481%   $260.7294   $260.73   $260.75   $260.70  
  7 purchase totals = $1,029.99       $1,126.3025   $1,126.30   $1,126.30   $1,126.30