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 $32.99   3.647%   $34.1931   $34.19   $34.20   $34.20  
  Purchase #2 $222.82   8.428%   $241.5993   $241.60   $241.60   $241.60  
  Purchase #3 $24.38   6.573%   $25.9825   $25.98   $26.00   $26.00  
  Purchase #4 $156.74   4.859%   $164.356   $164.36   $164.35   $164.40  
  Purchase #5 $149.95   7.861%   $161.7376   $161.74   $161.75   $161.70  
  Purchase #6 $109.98   12.207%   $123.4053   $123.41   $123.40   $123.40  
  Purchase #7 $217.93   5.858%   $230.6963   $230.70   $230.70   $230.70  
  7 purchase totals = $914.79       $981.9701   $981.98   $982.00   $982.00