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 $184.71   12.192%   $207.2298   $207.23   $207.25   $207.20  
  Purchase #2 $161.72   7.365%   $173.6307   $173.63   $173.65   $173.60  
  Purchase #3 $214.27   7.273%   $229.8539   $229.85   $229.85   $229.90  
  Purchase #4 $243.57   7.724%   $262.3833   $262.38   $262.40   $262.40  
  Purchase #5 $213.38   12.776%   $240.6414   $240.64   $240.65   $240.60  
  Purchase #6 $226.81   3.485%   $234.7143   $234.71   $234.70   $234.70  
  Purchase #7 $35.71   9.708%   $39.1767   $39.18   $39.20   $39.20  
  7 purchase totals = $1,280.17       $1,387.6301   $1,387.62   $1,387.70   $1,387.60