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 $110.38   11.840%   $123.449   $123.45   $123.45   $123.40  
  Purchase #2 $210.81   8.569%   $228.8743   $228.87   $228.85   $228.90  
  Purchase #3 $86.70   6.739%   $92.5427   $92.54   $92.55   $92.50  
  Purchase #4 $151.40   12.667%   $170.5778   $170.58   $170.60   $170.60  
  Purchase #5 $58.61   5.422%   $61.7878   $61.79   $61.80   $61.80  
  Purchase #6 $127.91   6.105%   $135.7189   $135.72   $135.70   $135.70  
  Purchase #7 $197.71   11.522%   $220.4901   $220.49   $220.50   $220.50  
  7 purchase totals = $943.52       $1,033.4406   $1,033.44   $1,033.45   $1,033.40