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 $65.26   8.695%   $70.9344   $70.93   $70.95   $70.90  
  Purchase #2 $120.42   8.517%   $130.6762   $130.68   $130.70   $130.70  
  Purchase #3 $161.54   8.397%   $175.1045   $175.10   $175.10   $175.10  
  Purchase #4 $19.95   13.385%   $22.6203   $22.62   $22.60   $22.60  
  Purchase #5 $225.43   8.596%   $244.808   $244.81   $244.80   $244.80  
  Purchase #6 $47.47   4.291%   $49.5069   $49.51   $49.50   $49.50  
  Purchase #7 $229.45   9.331%   $250.86   $250.86   $250.85   $250.90  
  7 purchase totals = $869.52       $944.5103   $944.51   $944.50   $944.50