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 $10.64   5.710%   $11.2475   $11.25   $11.25   $11.20  
  Purchase #2 $236.96   3.838%   $246.0545   $246.05   $246.05   $246.10  
  Purchase #3 $72.29   10.843%   $80.1284   $80.13   $80.15   $80.10  
  Purchase #4 $111.37   7.149%   $119.3318   $119.33   $119.35   $119.30  
  Purchase #5 $58.56   12.237%   $65.726   $65.73   $65.75   $65.70  
  Purchase #6 $186.84   6.444%   $198.88   $198.88   $198.90   $198.90  
  Purchase #7 $109.56   4.382%   $114.3609   $114.36   $114.35   $114.40  
  7 purchase totals = $786.22       $835.7291   $835.73   $835.80   $835.70