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 $162.25   11.623%   $181.1083   $181.11   $181.10   $181.10  
  Purchase #2 $194.57   4.798%   $203.9055   $203.91   $203.90   $203.90  
  Purchase #3 $40.87   6.509%   $43.5302   $43.53   $43.55   $43.50  
  Purchase #4 $59.75   3.510%   $61.8472   $61.85   $61.85   $61.80  
  Purchase #5 $241.58   10.361%   $266.6101   $266.61   $266.60   $266.60  
  Purchase #6 $243.67   12.647%   $274.4869   $274.49   $274.50   $274.50  
  Purchase #7 $241.75   7.545%   $259.99   $259.99   $260.00   $260.00  
  7 purchase totals = $1,184.44       $1,291.4782   $1,291.49   $1,291.50   $1,291.40