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 $250.66   8.871%   $272.896   $272.90   $272.90   $272.90  
  Purchase #2 $66.32   13.295%   $75.1372   $75.14   $75.15   $75.10  
  Purchase #3 $73.36   8.218%   $79.3887   $79.39   $79.40   $79.40  
  Purchase #4 $215.73   11.671%   $240.9078   $240.91   $240.90   $240.90  
  Purchase #5 $51.56   3.842%   $53.5409   $53.54   $53.55   $53.50  
  Purchase #6 $172.91   4.300%   $180.3451   $180.35   $180.35   $180.30  
  Purchase #7 $142.97   7.424%   $153.5841   $153.58   $153.60   $153.60  
  7 purchase totals = $973.51       $1,055.7998   $1,055.81   $1,055.85   $1,055.70