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 $61.28   12.534%   $68.9608   $68.96   $68.95   $69.00  
  Purchase #2 $175.87   4.724%   $184.1781   $184.18   $184.20   $184.20  
  Purchase #3 $191.90   8.241%   $207.7145   $207.71   $207.70   $207.70  
  Purchase #4 $58.62   12.326%   $65.8455   $65.85   $65.85   $65.80  
  Purchase #5 $58.34   10.250%   $64.3199   $64.32   $64.30   $64.30  
  Purchase #6 $35.84   8.688%   $38.9538   $38.95   $38.95   $39.00  
  Purchase #7 $74.49   4.221%   $77.6342   $77.63   $77.65   $77.60  
  7 purchase totals = $656.34       $707.6068   $707.60   $707.60   $707.60