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 $173.63   7.501%   $186.654   $186.65   $186.65   $186.70  
  Purchase #2 $16.84   4.756%   $17.6409   $17.64   $17.65   $17.60  
  Purchase #3 $213.73   7.500%   $229.7598   $229.76   $229.75   $229.80  
  Purchase #4 $152.57   10.827%   $169.0888   $169.09   $169.10   $169.10  
  Purchase #5 $84.94   10.118%   $93.5342   $93.53   $93.55   $93.50  
  Purchase #6 $148.81   11.128%   $165.3696   $165.37   $165.35   $165.40  
  Purchase #7 $196.56   3.436%   $203.3138   $203.31   $203.30   $203.30  
  7 purchase totals = $987.08       $1,065.3611   $1,065.35   $1,065.35   $1,065.40