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 $24.58   10.240%   $27.097   $27.10   $27.10   $27.10  
  Purchase #2 $206.80   6.583%   $220.4136   $220.41   $220.40   $220.40  
  Purchase #3 $179.38   11.676%   $200.3244   $200.32   $200.30   $200.30  
  Purchase #4 $216.75   8.594%   $235.3775   $235.38   $235.40   $235.40  
  Purchase #5 $203.85   11.144%   $226.567   $226.57   $226.55   $226.60  
  Purchase #6 $238.46   13.736%   $271.2149   $271.21   $271.20   $271.20  
  Purchase #7 $60.69   6.852%   $64.8485   $64.85   $64.85   $64.80  
  7 purchase totals = $1,130.51       $1,245.8429   $1,245.84   $1,245.80   $1,245.80