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 $189.97   7.697%   $204.592   $204.59   $204.60   $204.60  
  Purchase #2 $95.84   12.412%   $107.7357   $107.74   $107.75   $107.70  
  Purchase #3 $8.92   11.182%   $9.9174   $9.92   $9.90   $9.90  
  Purchase #4 $84.97   9.184%   $92.7736   $92.77   $92.75   $92.80  
  Purchase #5 $197.95   8.163%   $214.1087   $214.11   $214.10   $214.10  
  Purchase #6 $15.83   9.644%   $17.3566   $17.36   $17.35   $17.40  
  Purchase #7 $118.49   9.689%   $129.9705   $129.97   $129.95   $130.00  
  7 purchase totals = $711.97       $776.4545   $776.46   $776.40   $776.50