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 $245.81   3.788%   $255.1213   $255.12   $255.10   $255.10  
  Purchase #2 $150.56   8.613%   $163.5277   $163.53   $163.55   $163.50  
  Purchase #3 $34.55   4.749%   $36.1908   $36.19   $36.20   $36.20  
  Purchase #4 $203.73   4.636%   $213.1749   $213.17   $213.15   $213.20  
  Purchase #5 $113.94   3.254%   $117.6476   $117.65   $117.65   $117.60  
  Purchase #6 $181.43   11.302%   $201.9352   $201.94   $201.95   $201.90  
  Purchase #7 $145.91   12.179%   $163.6804   $163.68   $163.70   $163.70  
  7 purchase totals = $1,075.93       $1,151.2779   $1,151.28   $1,151.30   $1,151.20