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 $223.95   11.561%   $249.8409   $249.84   $249.85   $249.80  
  Purchase #2 $171.53   4.564%   $179.3586   $179.36   $179.35   $179.40  
  Purchase #3 $149.81   13.123%   $169.4696   $169.47   $169.45   $169.50  
  Purchase #4 $71.34   9.627%   $78.2079   $78.21   $78.20   $78.20  
  Purchase #5 $188.65   8.127%   $203.9816   $203.98   $204.00   $204.00  
  Purchase #6 $133.99   3.507%   $138.689   $138.69   $138.70   $138.70  
  Purchase #7 $165.91   12.102%   $185.9884   $185.99   $186.00   $186.00  
  7 purchase totals = $1,105.18       $1,205.5360   $1,205.54   $1,205.55   $1,205.60