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 $85.51   12.295%   $96.0235   $96.02   $96.00   $96.00  
  Purchase #2 $203.83   8.221%   $220.5869   $220.59   $220.60   $220.60  
  Purchase #3 $114.38   11.468%   $127.4971   $127.50   $127.50   $127.50  
  Purchase #4 $211.35   6.331%   $224.7306   $224.73   $224.75   $224.70  
  Purchase #5 $112.70   12.152%   $126.3953   $126.40   $126.40   $126.40  
  Purchase #6 $170.30   11.599%   $190.0531   $190.05   $190.05   $190.10  
  Purchase #7 $46.87   3.191%   $48.3656   $48.37   $48.35   $48.40  
  7 purchase totals = $944.94       $1,033.6521   $1,033.66   $1,033.65   $1,033.70