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 $64.31   6.659%   $68.5924   $68.59   $68.60   $68.60  
  Purchase #2 $83.70   6.767%   $89.364   $89.36   $89.35   $89.40  
  Purchase #3 $204.99   10.262%   $226.0261   $226.03   $226.05   $226.00  
  Purchase #4 $133.75   6.136%   $141.9569   $141.96   $141.95   $142.00  
  Purchase #5 $102.83   7.660%   $110.7068   $110.71   $110.70   $110.70  
  Purchase #6 $140.99   10.225%   $155.4062   $155.41   $155.40   $155.40  
  Purchase #7 $249.25   7.209%   $267.2184   $267.22   $267.20   $267.20  
  7 purchase totals = $979.82       $1,059.2708   $1,059.28   $1,059.25   $1,059.30