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 $206.71   8.185%   $223.6292   $223.63   $223.65   $223.60  
  Purchase #2 $144.35   7.345%   $154.9525   $154.95   $154.95   $155.00  
  Purchase #3 $239.46   12.186%   $268.6406   $268.64   $268.65   $268.60  
  Purchase #4 $150.32   10.167%   $165.603   $165.60   $165.60   $165.60  
  Purchase #5 $229.31   5.527%   $241.984   $241.98   $242.00   $242.00  
  Purchase #6 $189.43   8.751%   $206.007   $206.01   $206.00   $206.00  
  Purchase #7 $87.46   10.484%   $96.6293   $96.63   $96.65   $96.60  
  7 purchase totals = $1,247.04       $1,357.4456   $1,357.44   $1,357.50   $1,357.40