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 $167.94   10.726%   $185.9532   $185.95   $185.95   $186.00  
  Purchase #2 $110.73   7.352%   $118.8709   $118.87   $118.85   $118.90  
  Purchase #3 $133.61   7.832%   $144.0743   $144.07   $144.05   $144.10  
  Purchase #4 $229.44   10.748%   $254.1002   $254.10   $254.10   $254.10  
  Purchase #5 $17.49   13.411%   $19.8356   $19.84   $19.85   $19.80  
  Purchase #6 $214.43   9.263%   $234.2927   $234.29   $234.30   $234.30  
  Purchase #7 $243.60   5.747%   $257.5997   $257.60   $257.60   $257.60  
  7 purchase totals = $1,117.24       $1,214.7266   $1,214.72   $1,214.70   $1,214.80