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 $158.51   5.581%   $167.3564   $167.36   $167.35   $167.40  
  Purchase #2 $172.44   11.254%   $191.8464   $191.85   $191.85   $191.80  
  Purchase #3 $234.85   7.871%   $253.335   $253.34   $253.35   $253.30  
  Purchase #4 $12.88   10.376%   $14.2164   $14.22   $14.20   $14.20  
  Purchase #5 $67.62   3.349%   $69.8846   $69.88   $69.90   $69.90  
  Purchase #6 $87.60   7.606%   $94.2629   $94.26   $94.25   $94.30  
  Purchase #7 $224.99   12.152%   $252.3308   $252.33   $252.35   $252.30  
  7 purchase totals = $958.89       $1,043.2325   $1,043.24   $1,043.25   $1,043.20