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 $23.32   12.274%   $26.1823   $26.18   $26.20   $26.20  
  Purchase #2 $95.25   8.761%   $103.5949   $103.59   $103.60   $103.60  
  Purchase #3 $235.87   7.822%   $254.3198   $254.32   $254.30   $254.30  
  Purchase #4 $127.33   5.853%   $134.7826   $134.78   $134.80   $134.80  
  Purchase #5 $6.42   7.651%   $6.9112   $6.91   $6.90   $6.90  
  Purchase #6 $68.27   4.256%   $71.1756   $71.18   $71.20   $71.20  
  Purchase #7 $167.88   9.847%   $184.4111   $184.41   $184.40   $184.40  
  7 purchase totals = $724.34       $781.3775   $781.37   $781.40   $781.40