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 $31.95   5.429%   $33.6846   $33.68   $33.70   $33.70  
  Purchase #2 $107.30   10.560%   $118.6309   $118.63   $118.65   $118.60  
  Purchase #3 $218.62   8.163%   $236.466   $236.47   $236.45   $236.50  
  Purchase #4 $21.96   3.253%   $22.6744   $22.67   $22.65   $22.70  
  Purchase #5 $153.93   8.731%   $167.3696   $167.37   $167.35   $167.40  
  Purchase #6 $166.57   10.552%   $184.1465   $184.15   $184.15   $184.10  
  Purchase #7 $201.78   10.596%   $223.1606   $223.16   $223.15   $223.20  
  7 purchase totals = $902.11       $986.1326   $986.13   $986.10   $986.20