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 $61.43   9.479%   $67.2529   $67.25   $67.25   $67.30  
  Purchase #2 $193.89   3.777%   $201.2132   $201.21   $201.20   $201.20  
  Purchase #3 $244.70   4.166%   $254.8942   $254.89   $254.90   $254.90  
  Purchase #4 $28.59   11.651%   $31.921   $31.92   $31.90   $31.90  
  Purchase #5 $165.37   4.694%   $173.1325   $173.13   $173.15   $173.10  
  Purchase #6 $175.66   6.296%   $186.7196   $186.72   $186.70   $186.70  
  Purchase #7 $6.58   8.116%   $7.114   $7.11   $7.10   $7.10  
  7 purchase totals = $876.22       $922.2474   $922.23   $922.20   $922.20