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 $105.43   4.684%   $110.3683   $110.37   $110.35   $110.40  
  Purchase #2 $115.72   4.615%   $121.0605   $121.06   $121.05   $121.10  
  Purchase #3 $165.63   4.425%   $172.9591   $172.96   $172.95   $173.00  
  Purchase #4 $129.91   7.141%   $139.1869   $139.19   $139.20   $139.20  
  Purchase #5 $30.56   13.275%   $34.6168   $34.62   $34.60   $34.60  
  Purchase #6 $144.54   4.383%   $150.8752   $150.88   $150.90   $150.90  
  Purchase #7 $116.84   10.725%   $129.3711   $129.37   $129.35   $129.40  
  7 purchase totals = $808.63       $858.4379   $858.45   $858.40   $858.60