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 $208.69   11.716%   $233.1401   $233.14   $233.15   $233.10  
  Purchase #2 $114.99   11.331%   $128.0195   $128.02   $128.00   $128.00  
  Purchase #3 $37.28   5.442%   $39.3088   $39.31   $39.30   $39.30  
  Purchase #4 $145.96   4.388%   $152.3647   $152.36   $152.35   $152.40  
  Purchase #5 $86.99   7.809%   $93.783   $93.78   $93.80   $93.80  
  Purchase #6 $98.77   7.565%   $106.242   $106.24   $106.25   $106.20  
  Purchase #7 $170.73   8.107%   $184.5711   $184.57   $184.55   $184.60  
  7 purchase totals = $863.41       $937.4292   $937.42   $937.40   $937.40