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 $36.46   12.559%   $41.039   $41.04   $41.05   $41.00  
  Purchase #2 $46.32   11.839%   $51.8038   $51.80   $51.80   $51.80  
  Purchase #3 $95.53   10.743%   $105.7928   $105.79   $105.80   $105.80  
  Purchase #4 $236.93   6.440%   $252.1883   $252.19   $252.20   $252.20  
  Purchase #5 $32.33   5.871%   $34.2281   $34.23   $34.25   $34.20  
  Purchase #6 $119.41   6.819%   $127.5526   $127.55   $127.55   $127.60  
  Purchase #7 $79.71   4.756%   $83.501   $83.50   $83.50   $83.50  
  7 purchase totals = $646.69       $696.1056   $696.10   $696.15   $696.10