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 $32.90   5.113%   $34.5822   $34.58   $34.60   $34.60  
  Purchase #2 $222.95   11.810%   $249.2804   $249.28   $249.30   $249.30  
  Purchase #3 $154.96   10.113%   $170.6311   $170.63   $170.65   $170.60  
  Purchase #4 $163.77   11.391%   $182.425   $182.43   $182.45   $182.40  
  Purchase #5 $216.78   3.642%   $224.6751   $224.68   $224.70   $224.70  
  Purchase #6 $85.85   8.307%   $92.9816   $92.98   $93.00   $93.00  
  Purchase #7 $121.53   3.853%   $126.2126   $126.21   $126.20   $126.20  
  7 purchase totals = $998.74       $1,080.7880   $1,080.79   $1,080.90   $1,080.80