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 $233.60   3.209%   $241.0962   $241.10   $241.10   $241.10  
  Purchase #2 $26.87   11.145%   $29.8647   $29.86   $29.85   $29.90  
  Purchase #3 $110.46   9.122%   $120.5362   $120.54   $120.55   $120.50  
  Purchase #4 $184.60   12.714%   $208.07   $208.07   $208.05   $208.10  
  Purchase #5 $56.27   12.470%   $63.2869   $63.29   $63.30   $63.30  
  Purchase #6 $114.32   4.721%   $119.717   $119.72   $119.70   $119.70  
  Purchase #7 $143.98   13.400%   $163.2733   $163.27   $163.25   $163.30  
  7 purchase totals = $870.10       $945.8443   $945.85   $945.80   $945.90