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 $87.75   12.344%   $98.5819   $98.58   $98.60   $98.60  
  Purchase #2 $213.87   5.667%   $225.99   $225.99   $226.00   $226.00  
  Purchase #3 $145.33   5.433%   $153.2258   $153.23   $153.25   $153.20  
  Purchase #4 $136.66   3.771%   $141.8134   $141.81   $141.80   $141.80  
  Purchase #5 $132.25   8.565%   $143.5772   $143.58   $143.60   $143.60  
  Purchase #6 $72.96   7.137%   $78.1672   $78.17   $78.15   $78.20  
  Purchase #7 $190.26   9.757%   $208.8237   $208.82   $208.80   $208.80  
  7 purchase totals = $979.08       $1,050.1792   $1,050.18   $1,050.20   $1,050.20