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 $241.91   5.582%   $255.4134   $255.41   $255.40   $255.40  
  Purchase #2 $248.58   5.508%   $262.2718   $262.27   $262.25   $262.30  
  Purchase #3 $80.62   13.681%   $91.6496   $91.65   $91.65   $91.60  
  Purchase #4 $135.35   10.452%   $149.4968   $149.50   $149.50   $149.50  
  Purchase #5 $61.50   8.856%   $66.9464   $66.95   $66.95   $66.90  
  Purchase #6 $162.69   9.166%   $177.6022   $177.60   $177.60   $177.60  
  Purchase #7 $29.88   5.631%   $31.5625   $31.56   $31.55   $31.60  
  7 purchase totals = $960.53       $1,034.9427   $1,034.94   $1,034.90   $1,034.90