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 $88.67   11.808%   $99.1402   $99.14   $99.15   $99.10  
  Purchase #2 $141.60   11.320%   $157.6291   $157.63   $157.65   $157.60  
  Purchase #3 $191.74   6.585%   $204.3661   $204.37   $204.35   $204.40  
  Purchase #4 $244.58   7.296%   $262.4246   $262.42   $262.40   $262.40  
  Purchase #5 $239.33   11.372%   $266.5466   $266.55   $266.55   $266.50  
  Purchase #6 $110.67   12.610%   $124.6255   $124.63   $124.65   $124.60  
  Purchase #7 $12.92   7.294%   $13.8624   $13.86   $13.85   $13.90  
  7 purchase totals = $1,029.51       $1,128.5945   $1,128.60   $1,128.60   $1,128.50