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 $116.43   8.679%   $126.535   $126.54   $126.55   $126.50  
  Purchase #2 $217.50   8.847%   $236.7422   $236.74   $236.75   $236.70  
  Purchase #3 $28.30   6.531%   $30.1483   $30.15   $30.15   $30.10  
  Purchase #4 $113.28   4.579%   $118.4671   $118.47   $118.45   $118.50  
  Purchase #5 $119.79   12.575%   $134.8536   $134.85   $134.85   $134.90  
  Purchase #6 $232.68   9.264%   $254.2355   $254.24   $254.25   $254.20  
  Purchase #7 $37.58   4.521%   $39.279   $39.28   $39.30   $39.30  
  7 purchase totals = $865.56       $940.2607   $940.27   $940.30   $940.20