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 $158.59   6.566%   $169.003   $169.00   $169.00   $169.00  
  Purchase #2 $66.80   5.134%   $70.2295   $70.23   $70.25   $70.20  
  Purchase #3 $106.63   11.323%   $118.7037   $118.70   $118.70   $118.70  
  Purchase #4 $115.63   13.169%   $130.8573   $130.86   $130.85   $130.90  
  Purchase #5 $102.42   3.759%   $106.27   $106.27   $106.25   $106.30  
  Purchase #6 $174.77   11.654%   $195.1377   $195.14   $195.15   $195.10  
  Purchase #7 $109.80   10.783%   $121.6397   $121.64   $121.65   $121.60  
  7 purchase totals = $834.64       $911.8409   $911.84   $911.85   $911.80