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 $60.56   8.858%   $65.9244   $65.92   $65.90   $65.90  
  Purchase #2 $59.83   6.391%   $63.6537   $63.65   $63.65   $63.70  
  Purchase #3 $232.47   4.273%   $242.4034   $242.40   $242.40   $242.40  
  Purchase #4 $153.56   4.171%   $159.965   $159.97   $159.95   $160.00  
  Purchase #5 $216.44   9.623%   $237.268   $237.27   $237.25   $237.30  
  Purchase #6 $165.43   11.755%   $184.8763   $184.88   $184.90   $184.90  
  Purchase #7 $237.63   6.125%   $252.1848   $252.18   $252.20   $252.20  
  7 purchase totals = $1,125.92       $1,206.2756   $1,206.27   $1,206.25   $1,206.40