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 $113.87   8.298%   $123.3189   $123.32   $123.30   $123.30  
  Purchase #2 $250.51   8.841%   $272.6576   $272.66   $272.65   $272.70  
  Purchase #3 $37.54   13.331%   $42.5445   $42.54   $42.55   $42.50  
  Purchase #4 $230.97   5.794%   $244.3524   $244.35   $244.35   $244.40  
  Purchase #5 $246.44   6.234%   $261.8031   $261.80   $261.80   $261.80  
  Purchase #6 $42.86   10.378%   $47.308   $47.31   $47.30   $47.30  
  Purchase #7 $219.75   8.693%   $238.8529   $238.85   $238.85   $238.90  
  7 purchase totals = $1,141.94       $1,230.8374   $1,230.83   $1,230.80   $1,230.90