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 $202.75   13.826%   $230.7822   $230.78   $230.80   $230.80  
  Purchase #2 $174.51   13.598%   $198.2399   $198.24   $198.25   $198.20  
  Purchase #3 $187.43   13.723%   $213.151   $213.15   $213.15   $213.20  
  Purchase #4 $29.46   10.284%   $32.4897   $32.49   $32.50   $32.50  
  Purchase #5 $147.29   11.618%   $164.4022   $164.40   $164.40   $164.40  
  Purchase #6 $34.69   4.719%   $36.327   $36.33   $36.35   $36.30  
  Purchase #7 $142.34   12.340%   $159.9048   $159.90   $159.90   $159.90  
  7 purchase totals = $918.47       $1,035.2968   $1,035.29   $1,035.35   $1,035.30