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 $33.50   3.671%   $34.7298   $34.73   $34.75   $34.70  
  Purchase #2 $194.43   12.183%   $218.1174   $218.12   $218.10   $218.10  
  Purchase #3 $93.90   9.577%   $102.8928   $102.89   $102.90   $102.90  
  Purchase #4 $157.65   10.721%   $174.5517   $174.55   $174.55   $174.60  
  Purchase #5 $33.91   8.760%   $36.8805   $36.88   $36.90   $36.90  
  Purchase #6 $192.64   4.851%   $201.985   $201.99   $202.00   $202.00  
  Purchase #7 $197.47   8.185%   $213.6329   $213.63   $213.65   $213.60  
  7 purchase totals = $903.50       $982.7901   $982.79   $982.85   $982.80