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 $167.41   8.268%   $181.2515   $181.25   $181.25   $181.30  
  Purchase #2 $181.67   7.695%   $195.6495   $195.65   $195.65   $195.60  
  Purchase #3 $175.50   11.521%   $195.7194   $195.72   $195.70   $195.70  
  Purchase #4 $241.93   8.567%   $262.6561   $262.66   $262.65   $262.70  
  Purchase #5 $171.39   4.389%   $178.9123   $178.91   $178.90   $178.90  
  Purchase #6 $185.49   8.467%   $201.1954   $201.20   $201.20   $201.20  
  Purchase #7 $66.75   11.383%   $74.3482   $74.35   $74.35   $74.30  
  7 purchase totals = $1,190.14       $1,289.7324   $1,289.74   $1,289.70   $1,289.70