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 $60.51   4.723%   $63.3679   $63.37   $63.35   $63.40  
  Purchase #2 $89.67   3.375%   $92.6964   $92.70   $92.70   $92.70  
  Purchase #3 $81.84   5.465%   $86.3126   $86.31   $86.30   $86.30  
  Purchase #4 $95.93   6.589%   $102.2508   $102.25   $102.25   $102.30  
  Purchase #5 $115.69   9.589%   $126.7835   $126.78   $126.80   $126.80  
  Purchase #6 $22.51   9.159%   $24.5717   $24.57   $24.55   $24.60  
  Purchase #7 $103.76   5.647%   $109.6193   $109.62   $109.60   $109.60  
  7 purchase totals = $569.91       $605.6022   $605.60   $605.55   $605.70