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 $166.85   4.243%   $173.9294   $173.93   $173.95   $173.90  
  Purchase #2 $45.35   9.389%   $49.6079   $49.61   $49.60   $49.60  
  Purchase #3 $227.33   13.231%   $257.408   $257.41   $257.40   $257.40  
  Purchase #4 $119.86   5.561%   $126.5254   $126.53   $126.55   $126.50  
  Purchase #5 $223.51   7.667%   $240.6465   $240.65   $240.65   $240.60  
  Purchase #6 $247.72   4.825%   $259.6725   $259.67   $259.65   $259.70  
  Purchase #7 $84.55   10.476%   $93.4075   $93.41   $93.40   $93.40  
  7 purchase totals = $1,115.17       $1,201.1972   $1,201.21   $1,201.20   $1,201.10