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 $96.53   7.771%   $104.0313   $104.03   $104.05   $104.00  
  Purchase #2 $59.40   5.491%   $62.6617   $62.66   $62.65   $62.70  
  Purchase #3 $165.45   9.103%   $180.5109   $180.51   $180.50   $180.50  
  Purchase #4 $150.28   11.548%   $167.6343   $167.63   $167.65   $167.60  
  Purchase #5 $243.69   7.812%   $262.7271   $262.73   $262.75   $262.70  
  Purchase #6 $151.80   6.141%   $161.122   $161.12   $161.10   $161.10  
  Purchase #7 $110.96   5.265%   $116.802   $116.80   $116.80   $116.80  
  7 purchase totals = $978.11       $1,055.4893   $1,055.48   $1,055.50   $1,055.40