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 $171.61   7.546%   $184.5597   $184.56   $184.55   $184.60  
  Purchase #2 $160.35   3.854%   $166.5299   $166.53   $166.55   $166.50  
  Purchase #3 $184.56   6.190%   $195.9843   $195.98   $196.00   $196.00  
  Purchase #4 $89.59   7.379%   $96.2008   $96.20   $96.20   $96.20  
  Purchase #5 $150.69   8.441%   $163.4097   $163.41   $163.40   $163.40  
  Purchase #6 $204.44   12.857%   $230.7249   $230.72   $230.70   $230.70  
  Purchase #7 $151.44   11.709%   $169.1721   $169.17   $169.15   $169.20  
  7 purchase totals = $1,112.68       $1,206.5814   $1,206.57   $1,206.55   $1,206.60