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 $116.30   5.333%   $122.5023   $122.50   $122.50   $122.50  
  Purchase #2 $222.57   4.536%   $232.6658   $232.67   $232.65   $232.70  
  Purchase #3 $226.59   8.838%   $246.616   $246.62   $246.60   $246.60  
  Purchase #4 $244.69   11.732%   $273.397   $273.40   $273.40   $273.40  
  Purchase #5 $61.80   11.355%   $68.8174   $68.82   $68.80   $68.80  
  Purchase #6 $44.61   9.644%   $48.9122   $48.91   $48.90   $48.90  
  Purchase #7 $74.55   11.865%   $83.3954   $83.40   $83.40   $83.40  
  7 purchase totals = $991.11       $1,076.3061   $1,076.32   $1,076.25   $1,076.30