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 $61.91   3.107%   $63.8335   $63.83   $63.85   $63.80  
  Purchase #2 $30.69   10.139%   $33.8017   $33.80   $33.80   $33.80  
  Purchase #3 $20.49   13.208%   $23.1963   $23.20   $23.20   $23.20  
  Purchase #4 $200.70   12.136%   $225.057   $225.06   $225.05   $225.10  
  Purchase #5 $88.88   7.586%   $95.6224   $95.62   $95.60   $95.60  
  Purchase #6 $236.43   11.421%   $263.4327   $263.43   $263.45   $263.40  
  Purchase #7 $209.94   5.105%   $220.6574   $220.66   $220.65   $220.70  
  7 purchase totals = $849.04       $925.6010   $925.60   $925.60   $925.60