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 $236.49   5.365%   $249.1777   $249.18   $249.20   $249.20  
  Purchase #2 $241.73   10.763%   $267.7474   $267.75   $267.75   $267.70  
  Purchase #3 $163.61   5.576%   $172.7329   $172.73   $172.75   $172.70  
  Purchase #4 $175.63   9.808%   $192.8558   $192.86   $192.85   $192.90  
  Purchase #5 $56.77   4.290%   $59.2054   $59.21   $59.20   $59.20  
  Purchase #6 $22.52   9.766%   $24.7193   $24.72   $24.70   $24.70  
  Purchase #7 $49.67   6.681%   $52.9885   $52.99   $53.00   $53.00  
  7 purchase totals = $946.42       $1,019.4270   $1,019.44   $1,019.45   $1,019.40