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 $225.65   8.445%   $244.7061   $244.71   $244.70   $244.70  
  Purchase #2 $214.78   11.661%   $239.8255   $239.83   $239.85   $239.80  
  Purchase #3 $40.46   11.236%   $45.0061   $45.01   $45.00   $45.00  
  Purchase #4 $187.36   5.550%   $197.7585   $197.76   $197.75   $197.80  
  Purchase #5 $13.64   8.480%   $14.7967   $14.80   $14.80   $14.80  
  Purchase #6 $222.75   10.769%   $246.7379   $246.74   $246.75   $246.70  
  Purchase #7 $24.31   10.442%   $26.8485   $26.85   $26.85   $26.80  
  7 purchase totals = $928.95       $1,015.6793   $1,015.70   $1,015.70   $1,015.60