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 $63.63   6.176%   $67.5598   $67.56   $67.55   $67.60  
  Purchase #2 $198.80   13.351%   $225.3418   $225.34   $225.35   $225.30  
  Purchase #3 $44.78   8.301%   $48.4972   $48.50   $48.50   $48.50  
  Purchase #4 $142.75   8.712%   $155.1864   $155.19   $155.20   $155.20  
  Purchase #5 $84.63   7.145%   $90.6768   $90.68   $90.70   $90.70  
  Purchase #6 $189.82   5.232%   $199.7514   $199.75   $199.75   $199.80  
  Purchase #7 $229.85   12.114%   $257.694   $257.69   $257.70   $257.70  
  7 purchase totals = $954.26       $1,044.7074   $1,044.71   $1,044.75   $1,044.80