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 $151.93   10.412%   $167.749   $167.75   $167.75   $167.70  
  Purchase #2 $116.85   12.487%   $131.4411   $131.44   $131.45   $131.40  
  Purchase #3 $146.71   4.247%   $152.9408   $152.94   $152.95   $152.90  
  Purchase #4 $248.72   13.622%   $282.6006   $282.60   $282.60   $282.60  
  Purchase #5 $124.62   11.118%   $138.4753   $138.48   $138.50   $138.50  
  Purchase #6 $181.95   10.743%   $201.4969   $201.50   $201.50   $201.50  
  Purchase #7 $26.90   7.341%   $28.8747   $28.87   $28.85   $28.90  
  7 purchase totals = $997.68       $1,103.5784   $1,103.58   $1,103.60   $1,103.50