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 $56.49   3.687%   $58.5728   $58.57   $58.55   $58.60  
  Purchase #2 $244.39   3.151%   $252.0907   $252.09   $252.10   $252.10  
  Purchase #3 $163.35   9.195%   $178.37   $178.37   $178.35   $178.40  
  Purchase #4 $45.68   13.204%   $51.7116   $51.71   $51.70   $51.70  
  Purchase #5 $218.48   11.503%   $243.6118   $243.61   $243.60   $243.60  
  Purchase #6 $115.87   6.283%   $123.1501   $123.15   $123.15   $123.20  
  Purchase #7 $64.67   7.207%   $69.3308   $69.33   $69.35   $69.30  
  7 purchase totals = $908.93       $976.8378   $976.83   $976.80   $976.90