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 $108.48   9.836%   $119.1501   $119.15   $119.15   $119.20  
  Purchase #2 $230.39   12.632%   $259.4929   $259.49   $259.50   $259.50  
  Purchase #3 $160.72   10.494%   $177.586   $177.59   $177.60   $177.60  
  Purchase #4 $223.84   13.674%   $254.4479   $254.45   $254.45   $254.40  
  Purchase #5 $92.68   13.512%   $105.2029   $105.20   $105.20   $105.20  
  Purchase #6 $192.38   9.838%   $211.3063   $211.31   $211.30   $211.30  
  Purchase #7 $72.55   6.338%   $77.1482   $77.15   $77.15   $77.10  
  7 purchase totals = $1,081.04       $1,204.3343   $1,204.34   $1,204.35   $1,204.30