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 $88.54   8.413%   $95.9889   $95.99   $96.00   $96.00  
  Purchase #2 $223.28   4.488%   $233.3008   $233.30   $233.30   $233.30  
  Purchase #3 $64.91   3.695%   $67.3084   $67.31   $67.30   $67.30  
  Purchase #4 $131.74   7.312%   $141.3728   $141.37   $141.35   $141.40  
  Purchase #5 $132.31   11.503%   $147.5296   $147.53   $147.55   $147.50  
  Purchase #6 $92.34   4.152%   $96.174   $96.17   $96.15   $96.20  
  Purchase #7 $52.99   13.315%   $60.0456   $60.05   $60.05   $60.00  
  7 purchase totals = $786.11       $841.7201   $841.72   $841.70   $841.70