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 $246.60   7.788%   $265.8052   $265.81   $265.80   $265.80  
  Purchase #2 $145.95   10.240%   $160.8953   $160.90   $160.90   $160.90  
  Purchase #3 $221.49   5.727%   $234.1747   $234.17   $234.15   $234.20  
  Purchase #4 $152.88   10.682%   $169.2106   $169.21   $169.20   $169.20  
  Purchase #5 $244.71   4.562%   $255.8737   $255.87   $255.85   $255.90  
  Purchase #6 $57.33   10.376%   $63.2786   $63.28   $63.30   $63.30  
  Purchase #7 $35.90   3.133%   $37.0247   $37.02   $37.00   $37.00  
  7 purchase totals = $1,104.86       $1,186.2628   $1,186.26   $1,186.20   $1,186.30