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 $76.70   8.191%   $82.9825   $82.98   $83.00   $83.00  
  Purchase #2 $141.72   8.544%   $153.8286   $153.83   $153.85   $153.80  
  Purchase #3 $126.69   11.180%   $140.8539   $140.85   $140.85   $140.90  
  Purchase #4 $57.96   6.552%   $61.7575   $61.76   $61.75   $61.80  
  Purchase #5 $118.76   9.228%   $129.7192   $129.72   $129.70   $129.70  
  Purchase #6 $181.62   9.485%   $198.8467   $198.85   $198.85   $198.80  
  Purchase #7 $148.43   4.802%   $155.5576   $155.56   $155.55   $155.60  
  7 purchase totals = $851.88       $923.5460   $923.55   $923.55   $923.60