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 $234.41   12.171%   $262.94   $262.94   $262.95   $262.90  
  Purchase #2 $225.41   13.720%   $256.3363   $256.34   $256.35   $256.30  
  Purchase #3 $51.48   3.523%   $53.2936   $53.29   $53.30   $53.30  
  Purchase #4 $152.73   13.289%   $173.0263   $173.03   $173.05   $173.00  
  Purchase #5 $88.93   7.525%   $95.622   $95.62   $95.60   $95.60  
  Purchase #6 $148.58   8.409%   $161.0741   $161.07   $161.05   $161.10  
  Purchase #7 $154.57   8.612%   $167.8816   $167.88   $167.90   $167.90  
  7 purchase totals = $1,056.11       $1,170.1739   $1,170.17   $1,170.20   $1,170.10