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 $72.40   3.636%   $75.0325   $75.03   $75.05   $75.00  
  Purchase #2 $223.65   11.366%   $249.0701   $249.07   $249.05   $249.10  
  Purchase #3 $52.60   5.279%   $55.3768   $55.38   $55.40   $55.40  
  Purchase #4 $84.37   8.701%   $91.711   $91.71   $91.70   $91.70  
  Purchase #5 $248.34   9.137%   $271.0308   $271.03   $271.05   $271.00  
  Purchase #6 $208.32   8.377%   $225.771   $225.77   $225.75   $225.80  
  Purchase #7 $163.46   6.479%   $174.0506   $174.05   $174.05   $174.10  
  7 purchase totals = $1,053.14       $1,142.0428   $1,142.04   $1,142.05   $1,142.10