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 $68.27   12.387%   $76.7266   $76.73   $76.75   $76.70  
  Purchase #2 $213.56   6.784%   $228.0479   $228.05   $228.05   $228.00  
  Purchase #3 $127.60   9.834%   $140.1482   $140.15   $140.15   $140.10  
  Purchase #4 $196.95   13.604%   $223.7431   $223.74   $223.75   $223.70  
  Purchase #5 $112.76   13.417%   $127.889   $127.89   $127.90   $127.90  
  Purchase #6 $176.55   4.815%   $185.0509   $185.05   $185.05   $185.10  
  Purchase #7 $209.42   11.134%   $232.7368   $232.74   $232.75   $232.70  
  7 purchase totals = $1,105.11       $1,214.3425   $1,214.35   $1,214.40   $1,214.20