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 $239.62   12.607%   $269.8289   $269.83   $269.85   $269.80  
  Purchase #2 $155.58   7.321%   $166.97   $166.97   $166.95   $167.00  
  Purchase #3 $69.59   3.253%   $71.8538   $71.85   $71.85   $71.90  
  Purchase #4 $84.48   11.529%   $94.2197   $94.22   $94.20   $94.20  
  Purchase #5 $24.29   6.598%   $25.8927   $25.89   $25.90   $25.90  
  Purchase #6 $110.71   11.872%   $123.8535   $123.85   $123.85   $123.90  
  Purchase #7 $114.76   12.706%   $129.3414   $129.34   $129.35   $129.30  
  7 purchase totals = $799.03       $881.9600   $881.95   $881.95   $882.00