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 $250.62   3.463%   $259.299   $259.30   $259.30   $259.30  
  Purchase #2 $68.96   10.803%   $76.4097   $76.41   $76.40   $76.40  
  Purchase #3 $99.60   8.322%   $107.8887   $107.89   $107.90   $107.90  
  Purchase #4 $141.97   7.196%   $152.1862   $152.19   $152.20   $152.20  
  Purchase #5 $157.53   6.208%   $167.3095   $167.31   $167.30   $167.30  
  Purchase #6 $231.34   6.474%   $246.317   $246.32   $246.30   $246.30  
  Purchase #7 $112.52   9.741%   $123.4806   $123.48   $123.50   $123.50  
  7 purchase totals = $1,062.54       $1,132.8907   $1,132.90   $1,132.90   $1,132.90