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 $161.96   13.393%   $183.6513   $183.65   $183.65   $183.70  
  Purchase #2 $60.83   3.304%   $62.8398   $62.84   $62.85   $62.80  
  Purchase #3 $161.37   9.511%   $176.7179   $176.72   $176.70   $176.70  
  Purchase #4 $168.62   3.699%   $174.8573   $174.86   $174.85   $174.90  
  Purchase #5 $185.72   10.466%   $205.1575   $205.16   $205.15   $205.20  
  Purchase #6 $64.34   7.523%   $69.1803   $69.18   $69.20   $69.20  
  Purchase #7 $161.98   9.108%   $176.7331   $176.73   $176.75   $176.70  
  7 purchase totals = $964.82       $1,049.1372   $1,049.14   $1,049.15   $1,049.20