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 $146.81   11.434%   $163.5963   $163.60   $163.60   $163.60  
  Purchase #2 $64.47   4.332%   $67.2628   $67.26   $67.25   $67.30  
  Purchase #3 $229.26   7.523%   $246.5072   $246.51   $246.50   $246.50  
  Purchase #4 $94.80   11.608%   $105.8044   $105.80   $105.80   $105.80  
  Purchase #5 $241.51   13.845%   $274.9471   $274.95   $274.95   $274.90  
  Purchase #6 $153.95   8.123%   $166.4554   $166.46   $166.45   $166.50  
  Purchase #7 $40.54   9.482%   $44.384   $44.38   $44.40   $44.40  
  7 purchase totals = $971.34       $1,068.9572   $1,068.96   $1,068.95   $1,069.00