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 $68.97   12.849%   $77.832   $77.83   $77.85   $77.80  
  Purchase #2 $247.75   10.176%   $272.961   $272.96   $272.95   $273.00  
  Purchase #3 $111.65   8.748%   $121.4171   $121.42   $121.40   $121.40  
  Purchase #4 $179.31   6.412%   $190.8074   $190.81   $190.80   $190.80  
  Purchase #5 $47.50   11.351%   $52.8917   $52.89   $52.90   $52.90  
  Purchase #6 $116.46   11.230%   $129.5385   $129.54   $129.55   $129.50  
  Purchase #7 $169.60   6.126%   $179.9897   $179.99   $180.00   $180.00  
  7 purchase totals = $941.24       $1,025.4374   $1,025.44   $1,025.45   $1,025.40