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 $188.83   13.306%   $213.9557   $213.96   $213.95   $214.00  
  Purchase #2 $162.40   9.336%   $177.5617   $177.56   $177.55   $177.60  
  Purchase #3 $246.73   8.604%   $267.9586   $267.96   $267.95   $268.00  
  Purchase #4 $212.98   5.215%   $224.0869   $224.09   $224.10   $224.10  
  Purchase #5 $162.56   5.680%   $171.7934   $171.79   $171.80   $171.80  
  Purchase #6 $133.85   11.200%   $148.8412   $148.84   $148.85   $148.80  
  Purchase #7 $5.36   13.264%   $6.071   $6.07   $6.05   $6.10  
  7 purchase totals = $1,112.71       $1,210.2685   $1,210.27   $1,210.25   $1,210.40