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 $53.96   4.651%   $56.4697   $56.47   $56.45   $56.50  
  Purchase #2 $121.51   3.372%   $125.6073   $125.61   $125.60   $125.60  
  Purchase #3 $104.66   13.133%   $118.405   $118.41   $118.40   $118.40  
  Purchase #4 $151.98   6.546%   $161.9286   $161.93   $161.95   $161.90  
  Purchase #5 $179.44   5.444%   $189.2087   $189.21   $189.20   $189.20  
  Purchase #6 $163.86   4.830%   $171.7744   $171.77   $171.75   $171.80  
  Purchase #7 $22.32   8.554%   $24.2293   $24.23   $24.25   $24.20  
  7 purchase totals = $797.73       $847.6230   $847.63   $847.60   $847.60