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 $91.97   4.827%   $96.4094   $96.41   $96.40   $96.40  
  Purchase #2 $20.65   13.176%   $23.3708   $23.37   $23.35   $23.40  
  Purchase #3 $246.90   7.580%   $265.615   $265.62   $265.60   $265.60  
  Purchase #4 $37.82   8.857%   $41.1697   $41.17   $41.15   $41.20  
  Purchase #5 $87.44   4.137%   $91.0574   $91.06   $91.05   $91.10  
  Purchase #6 $67.53   10.194%   $74.414   $74.41   $74.40   $74.40  
  Purchase #7 $209.62   8.401%   $227.2302   $227.23   $227.25   $227.20  
  7 purchase totals = $761.93       $819.2665   $819.27   $819.20   $819.30