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 $229.61   8.336%   $248.7503   $248.75   $248.75   $248.80  
  Purchase #2 $63.40   13.529%   $71.9774   $71.98   $72.00   $72.00  
  Purchase #3 $171.54   13.303%   $194.36   $194.36   $194.35   $194.40  
  Purchase #4 $40.76   9.498%   $44.6314   $44.63   $44.65   $44.60  
  Purchase #5 $226.81   3.417%   $234.5601   $234.56   $234.55   $234.60  
  Purchase #6 $230.80   8.729%   $250.9465   $250.95   $250.95   $250.90  
  Purchase #7 $153.50   6.305%   $163.1782   $163.18   $163.20   $163.20  
  7 purchase totals = $1,116.42       $1,208.4039   $1,208.41   $1,208.45   $1,208.50