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 $82.37   7.226%   $88.3221   $88.32   $88.30   $88.30  
  Purchase #2 $237.49   11.767%   $265.4354   $265.44   $265.45   $265.40  
  Purchase #3 $156.32   3.257%   $161.4113   $161.41   $161.40   $161.40  
  Purchase #4 $105.91   12.837%   $119.5057   $119.51   $119.50   $119.50  
  Purchase #5 $229.49   13.112%   $259.5807   $259.58   $259.60   $259.60  
  Purchase #6 $134.94   8.187%   $145.9875   $145.99   $146.00   $146.00  
  Purchase #7 $194.55   13.251%   $220.3298   $220.33   $220.35   $220.30  
  7 purchase totals = $1,141.07       $1,260.5725   $1,260.58   $1,260.60   $1,260.50