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 $116.36   12.745%   $131.1901   $131.19   $131.20   $131.20  
  Purchase #2 $147.32   13.120%   $166.6484   $166.65   $166.65   $166.60  
  Purchase #3 $140.64   7.536%   $151.2386   $151.24   $151.25   $151.20  
  Purchase #4 $201.43   9.842%   $221.2547   $221.25   $221.25   $221.30  
  Purchase #5 $48.64   11.285%   $54.129   $54.13   $54.15   $54.10  
  Purchase #6 $185.49   9.518%   $203.1449   $203.14   $203.15   $203.10  
  Purchase #7 $67.40   3.209%   $69.5629   $69.56   $69.55   $69.60  
  7 purchase totals = $907.28       $997.1686   $997.16   $997.20   $997.10