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 $188.82   13.567%   $214.4372   $214.44   $214.45   $214.40  
  Purchase #2 $215.71   6.408%   $229.5327   $229.53   $229.55   $229.50  
  Purchase #3 $97.89   8.708%   $106.4143   $106.41   $106.40   $106.40  
  Purchase #4 $215.27   8.853%   $234.3279   $234.33   $234.35   $234.30  
  Purchase #5 $246.99   3.458%   $255.5309   $255.53   $255.55   $255.50  
  Purchase #6 $113.36   4.132%   $118.044   $118.04   $118.05   $118.00  
  Purchase #7 $125.41   12.610%   $141.2242   $141.22   $141.20   $141.20  
  7 purchase totals = $1,203.45       $1,299.5112   $1,299.50   $1,299.55   $1,299.30