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 $38.56   6.455%   $41.049   $41.05   $41.05   $41.00  
  Purchase #2 $43.54   11.467%   $48.5327   $48.53   $48.55   $48.50  
  Purchase #3 $187.75   4.394%   $195.9997   $196.00   $196.00   $196.00  
  Purchase #4 $162.77   8.203%   $176.122   $176.12   $176.10   $176.10  
  Purchase #5 $118.51   6.562%   $126.2866   $126.29   $126.30   $126.30  
  Purchase #6 $209.42   10.399%   $231.1976   $231.20   $231.20   $231.20  
  Purchase #7 $201.86   6.253%   $214.4823   $214.48   $214.50   $214.50  
  7 purchase totals = $962.41       $1,033.6699   $1,033.67   $1,033.70   $1,033.60