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 $61.56   6.634%   $65.6439   $65.64   $65.65   $65.60  
  Purchase #2 $181.98   7.717%   $196.0234   $196.02   $196.00   $196.00  
  Purchase #3 $240.64   9.575%   $263.6813   $263.68   $263.70   $263.70  
  Purchase #4 $250.25   10.503%   $276.5338   $276.53   $276.55   $276.50  
  Purchase #5 $109.81   3.137%   $113.2547   $113.25   $113.25   $113.30  
  Purchase #6 $166.64   11.659%   $186.0686   $186.07   $186.05   $186.10  
  Purchase #7 $108.37   9.165%   $118.3021   $118.30   $118.30   $118.30  
  7 purchase totals = $1,119.25       $1,219.5078   $1,219.49   $1,219.50   $1,219.50