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 $75.81   10.488%   $83.761   $83.76   $83.75   $83.80  
  Purchase #2 $112.40   6.305%   $119.4868   $119.49   $119.50   $119.50  
  Purchase #3 $59.29   13.150%   $67.0866   $67.09   $67.10   $67.10  
  Purchase #4 $151.89   12.241%   $170.4829   $170.48   $170.50   $170.50  
  Purchase #5 $62.86   4.482%   $65.6774   $65.68   $65.70   $65.70  
  Purchase #6 $225.51   7.361%   $242.1098   $242.11   $242.10   $242.10  
  Purchase #7 $198.26   6.277%   $210.7048   $210.70   $210.70   $210.70  
  7 purchase totals = $886.02       $959.3093   $959.31   $959.35   $959.40