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 $86.53   11.733%   $96.6826   $96.68   $96.70   $96.70  
  Purchase #2 $164.61   6.339%   $175.0446   $175.04   $175.05   $175.00  
  Purchase #3 $149.41   11.532%   $166.64   $166.64   $166.65   $166.60  
  Purchase #4 $39.94   7.817%   $43.0621   $43.06   $43.05   $43.10  
  Purchase #5 $199.91   8.223%   $216.3486   $216.35   $216.35   $216.30  
  Purchase #6 $206.63   9.837%   $226.9562   $226.96   $226.95   $227.00  
  Purchase #7 $48.72   8.371%   $52.7984   $52.80   $52.80   $52.80  
  7 purchase totals = $895.75       $977.5325   $977.53   $977.55   $977.50