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 $204.51   9.535%   $224.01   $224.01   $224.00   $224.00  
  Purchase #2 $115.53   5.335%   $121.6935   $121.69   $121.70   $121.70  
  Purchase #3 $14.42   6.776%   $15.3971   $15.40   $15.40   $15.40  
  Purchase #4 $26.47   5.139%   $27.8303   $27.83   $27.85   $27.80  
  Purchase #5 $204.81   6.579%   $218.2844   $218.28   $218.30   $218.30  
  Purchase #6 $62.79   12.510%   $70.645   $70.65   $70.65   $70.60  
  Purchase #7 $142.58   12.543%   $160.4638   $160.46   $160.45   $160.50  
  7 purchase totals = $771.11       $838.3241   $838.32   $838.35   $838.30