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 $86.71   11.315%   $96.5212   $96.52   $96.50   $96.50  
  Purchase #2 $8.67   8.872%   $9.4392   $9.44   $9.45   $9.40  
  Purchase #3 $41.73   10.224%   $45.9965   $46.00   $46.00   $46.00  
  Purchase #4 $244.43   13.350%   $277.0614   $277.06   $277.05   $277.10  
  Purchase #5 $56.81   8.151%   $61.4406   $61.44   $61.45   $61.40  
  Purchase #6 $226.70   3.218%   $233.9952   $234.00   $234.00   $234.00  
  Purchase #7 $115.35   6.160%   $122.4556   $122.46   $122.45   $122.50  
  7 purchase totals = $780.40       $846.9097   $846.92   $846.90   $846.90