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 $108.51   9.731%   $119.0691   $119.07   $119.05   $119.10  
  Purchase #2 $16.85   12.356%   $18.932   $18.93   $18.95   $18.90  
  Purchase #3 $47.33   5.549%   $49.9563   $49.96   $49.95   $50.00  
  Purchase #4 $114.59   4.320%   $119.5403   $119.54   $119.55   $119.50  
  Purchase #5 $205.43   6.301%   $218.3741   $218.37   $218.35   $218.40  
  Purchase #6 $89.91   6.761%   $95.9888   $95.99   $96.00   $96.00  
  Purchase #7 $73.66   11.382%   $82.044   $82.04   $82.05   $82.00  
  7 purchase totals = $656.28       $703.9046   $703.90   $703.90   $703.90