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 $54.92   10.329%   $60.5927   $60.59   $60.60   $60.60  
  Purchase #2 $104.92   6.195%   $111.4198   $111.42   $111.40   $111.40  
  Purchase #3 $151.31   9.277%   $165.347   $165.35   $165.35   $165.30  
  Purchase #4 $76.45   4.758%   $80.0875   $80.09   $80.10   $80.10  
  Purchase #5 $163.73   3.644%   $169.6963   $169.70   $169.70   $169.70  
  Purchase #6 $141.63   8.223%   $153.2762   $153.28   $153.30   $153.30  
  Purchase #7 $127.92   3.297%   $132.1375   $132.14   $132.15   $132.10  
  7 purchase totals = $820.88       $872.5570   $872.57   $872.60   $872.50