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 $154.25   13.834%   $175.5889   $175.59   $175.60   $175.60  
  Purchase #2 $35.75   8.428%   $38.763   $38.76   $38.75   $38.80  
  Purchase #3 $16.44   10.503%   $18.1667   $18.17   $18.15   $18.20  
  Purchase #4 $59.39   6.296%   $63.1292   $63.13   $63.15   $63.10  
  Purchase #5 $207.52   8.692%   $225.5576   $225.56   $225.55   $225.60  
  Purchase #6 $249.85   7.768%   $269.2583   $269.26   $269.25   $269.30  
  Purchase #7 $69.29   7.105%   $74.2131   $74.21   $74.20   $74.20  
  7 purchase totals = $792.49       $864.6768   $864.68   $864.65   $864.80