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 $200.36   9.244%   $218.8813   $218.88   $218.90   $218.90  
  Purchase #2 $158.64   8.563%   $172.2243   $172.22   $172.20   $172.20  
  Purchase #3 $153.33   5.827%   $162.2645   $162.26   $162.25   $162.30  
  Purchase #4 $126.39   5.349%   $133.1506   $133.15   $133.15   $133.20  
  Purchase #5 $215.69   7.270%   $231.3707   $231.37   $231.35   $231.40  
  Purchase #6 $85.65   11.145%   $95.1957   $95.20   $95.20   $95.20  
  Purchase #7 $194.96   11.770%   $217.9068   $217.91   $217.90   $217.90  
  7 purchase totals = $1,135.02       $1,230.9939   $1,230.99   $1,230.95   $1,231.10