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 $87.48   10.685%   $96.8272   $96.83   $96.85   $96.80  
  Purchase #2 $114.53   5.124%   $120.3985   $120.40   $120.40   $120.40  
  Purchase #3 $39.75   11.126%   $44.1726   $44.17   $44.15   $44.20  
  Purchase #4 $110.46   5.729%   $116.7883   $116.79   $116.80   $116.80  
  Purchase #5 $55.89   11.143%   $62.1178   $62.12   $62.10   $62.10  
  Purchase #6 $193.95   6.651%   $206.8496   $206.85   $206.85   $206.80  
  Purchase #7 $51.69   8.394%   $56.0289   $56.03   $56.05   $56.00  
  7 purchase totals = $653.75       $703.1829   $703.19   $703.20   $703.10