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 $113.39   8.521%   $123.052   $123.05   $123.05   $123.10  
  Purchase #2 $224.32   6.397%   $238.6698   $238.67   $238.65   $238.70  
  Purchase #3 $59.26   10.844%   $65.6862   $65.69   $65.70   $65.70  
  Purchase #4 $93.51   11.126%   $103.9139   $103.91   $103.90   $103.90  
  Purchase #5 $170.90   9.394%   $186.9543   $186.95   $186.95   $187.00  
  Purchase #6 $122.78   4.461%   $128.2572   $128.26   $128.25   $128.30  
  Purchase #7 $103.51   3.283%   $106.9082   $106.91   $106.90   $106.90  
  7 purchase totals = $887.67       $953.4416   $953.44   $953.40   $953.60