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 $205.66   12.404%   $231.1701   $231.17   $231.15   $231.20  
  Purchase #2 $202.62   8.102%   $219.0363   $219.04   $219.05   $219.00  
  Purchase #3 $69.33   8.354%   $75.1218   $75.12   $75.10   $75.10  
  Purchase #4 $184.64   12.785%   $208.2462   $208.25   $208.25   $208.20  
  Purchase #5 $48.98   6.587%   $52.2063   $52.21   $52.20   $52.20  
  Purchase #6 $196.76   4.789%   $206.1828   $206.18   $206.20   $206.20  
  Purchase #7 $116.83   8.828%   $127.1438   $127.14   $127.15   $127.10  
  7 purchase totals = $1,024.82       $1,119.1073   $1,119.11   $1,119.10   $1,119.00