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 $169.42   8.814%   $184.3527   $184.35   $184.35   $184.40  
  Purchase #2 $70.44   8.861%   $76.6817   $76.68   $76.70   $76.70  
  Purchase #3 $185.32   10.517%   $204.8101   $204.81   $204.80   $204.80  
  Purchase #4 $12.76   12.480%   $14.3524   $14.35   $14.35   $14.40  
  Purchase #5 $118.51   11.215%   $131.8009   $131.80   $131.80   $131.80  
  Purchase #6 $161.75   13.675%   $183.8693   $183.87   $183.85   $183.90  
  Purchase #7 $216.30   6.699%   $230.7899   $230.79   $230.80   $230.80  
  7 purchase totals = $934.50       $1,026.6570   $1,026.65   $1,026.65   $1,026.80