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 $60.72   6.691%   $64.7828   $64.78   $64.80   $64.80  
  Purchase #2 $158.66   13.263%   $179.7031   $179.70   $179.70   $179.70  
  Purchase #3 $127.97   3.687%   $132.6883   $132.69   $132.70   $132.70  
  Purchase #4 $143.47   6.575%   $152.9032   $152.90   $152.90   $152.90  
  Purchase #5 $82.90   6.106%   $87.9619   $87.96   $87.95   $88.00  
  Purchase #6 $116.97   5.861%   $123.8256   $123.83   $123.85   $123.80  
  Purchase #7 $107.81   7.196%   $115.568   $115.57   $115.55   $115.60  
  7 purchase totals = $798.50       $857.4329   $857.43   $857.45   $857.50