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 $247.93   13.758%   $282.0402   $282.04   $282.05   $282.00  
  Purchase #2 $63.54   8.167%   $68.7293   $68.73   $68.75   $68.70  
  Purchase #3 $28.51   13.168%   $32.2642   $32.26   $32.25   $32.30  
  Purchase #4 $239.96   11.196%   $266.8259   $266.83   $266.85   $266.80  
  Purchase #5 $245.97   12.519%   $276.763   $276.76   $276.75   $276.80  
  Purchase #6 $250.67   8.184%   $271.1848   $271.18   $271.20   $271.20  
  Purchase #7 $219.39   13.410%   $248.8102   $248.81   $248.80   $248.80  
  7 purchase totals = $1,295.97       $1,446.6176   $1,446.61   $1,446.65   $1,446.60