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 $77.99   7.477%   $83.8213   $83.82   $83.80   $83.80  
  Purchase #2 $116.96   6.845%   $124.9659   $124.97   $124.95   $125.00  
  Purchase #3 $63.26   12.109%   $70.9202   $70.92   $70.90   $70.90  
  Purchase #4 $249.57   5.861%   $264.1973   $264.20   $264.20   $264.20  
  Purchase #5 $27.64   4.661%   $28.9283   $28.93   $28.95   $28.90  
  Purchase #6 $192.81   10.441%   $212.9413   $212.94   $212.95   $212.90  
  Purchase #7 $161.42   5.614%   $170.4821   $170.48   $170.50   $170.50  
  7 purchase totals = $889.65       $956.2564   $956.26   $956.25   $956.20