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 $61.27   6.772%   $65.4192   $65.42   $65.40   $65.40  
  Purchase #2 $98.86   8.372%   $107.1366   $107.14   $107.15   $107.10  
  Purchase #3 $55.81   7.752%   $60.1364   $60.14   $60.15   $60.10  
  Purchase #4 $75.39   11.288%   $83.9   $83.90   $83.90   $83.90  
  Purchase #5 $52.45   11.443%   $58.4519   $58.45   $58.45   $58.50  
  Purchase #6 $173.79   11.643%   $194.0244   $194.02   $194.00   $194.00  
  Purchase #7 $181.69   8.292%   $196.7557   $196.76   $196.75   $196.80  
  7 purchase totals = $699.26       $765.8242   $765.83   $765.80   $765.80