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 $94.81   3.594%   $98.2175   $98.22   $98.20   $98.20  
  Purchase #2 $65.28   12.779%   $73.6221   $73.62   $73.60   $73.60  
  Purchase #3 $26.68   11.729%   $29.8093   $29.81   $29.80   $29.80  
  Purchase #4 $91.72   7.517%   $98.6146   $98.61   $98.60   $98.60  
  Purchase #5 $212.63   8.773%   $231.284   $231.28   $231.30   $231.30  
  Purchase #6 $246.64   6.799%   $263.4091   $263.41   $263.40   $263.40  
  Purchase #7 $47.64   4.590%   $49.8267   $49.83   $49.85   $49.80  
  7 purchase totals = $785.40       $844.7833   $844.78   $844.75   $844.70