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 $24.63   9.669%   $27.0115   $27.01   $27.00   $27.00  
  Purchase #2 $186.67   13.174%   $211.2619   $211.26   $211.25   $211.30  
  Purchase #3 $139.70   9.699%   $153.2495   $153.25   $153.25   $153.20  
  Purchase #4 $184.59   6.604%   $196.7803   $196.78   $196.80   $196.80  
  Purchase #5 $228.91   7.144%   $245.2633   $245.26   $245.25   $245.30  
  Purchase #6 $250.90   13.142%   $283.8733   $283.87   $283.85   $283.90  
  Purchase #7 $159.54   10.618%   $176.48   $176.48   $176.50   $176.50  
  7 purchase totals = $1,174.94       $1,293.9198   $1,293.91   $1,293.90   $1,294.00