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 $202.42   10.476%   $223.6255   $223.63   $223.65   $223.60  
  Purchase #2 $86.72   11.693%   $96.8602   $96.86   $96.85   $96.90  
  Purchase #3 $162.60   13.829%   $185.086   $185.09   $185.10   $185.10  
  Purchase #4 $106.35   5.393%   $112.0855   $112.09   $112.10   $112.10  
  Purchase #5 $167.29   12.486%   $188.1778   $188.18   $188.20   $188.20  
  Purchase #6 $240.37   9.709%   $263.7075   $263.71   $263.70   $263.70  
  Purchase #7 $139.94   3.403%   $144.7022   $144.70   $144.70   $144.70  
  7 purchase totals = $1,105.69       $1,214.2447   $1,214.26   $1,214.30   $1,214.30