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 $90.51   5.159%   $95.1794   $95.18   $95.20   $95.20  
  Purchase #2 $152.79   7.359%   $164.0338   $164.03   $164.05   $164.00  
  Purchase #3 $33.39   11.394%   $37.1945   $37.19   $37.20   $37.20  
  Purchase #4 $215.36   4.132%   $224.2587   $224.26   $224.25   $224.30  
  Purchase #5 $73.50   9.697%   $80.6273   $80.63   $80.65   $80.60  
  Purchase #6 $192.46   5.559%   $203.1589   $203.16   $203.15   $203.20  
  Purchase #7 $51.45   9.120%   $56.1422   $56.14   $56.15   $56.10  
  7 purchase totals = $809.46       $860.5948   $860.59   $860.65   $860.60