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 $214.77   12.650%   $241.9384   $241.94   $241.95   $241.90  
  Purchase #2 $110.40   11.841%   $123.4725   $123.47   $123.45   $123.50  
  Purchase #3 $155.61   13.309%   $176.3201   $176.32   $176.30   $176.30  
  Purchase #4 $188.76   7.665%   $203.2285   $203.23   $203.25   $203.20  
  Purchase #5 $244.91   7.244%   $262.6513   $262.65   $262.65   $262.70  
  Purchase #6 $63.57   8.477%   $68.9588   $68.96   $68.95   $69.00  
  Purchase #7 $140.79   12.426%   $158.2846   $158.28   $158.30   $158.30  
  7 purchase totals = $1,118.81       $1,234.8542   $1,234.85   $1,234.85   $1,234.90