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 $86.52   10.457%   $95.5674   $95.57   $95.55   $95.60  
  Purchase #2 $111.85   6.363%   $118.967   $118.97   $118.95   $119.00  
  Purchase #3 $6.57   3.277%   $6.7853   $6.79   $6.80   $6.80  
  Purchase #4 $70.33   12.231%   $78.9321   $78.93   $78.95   $78.90  
  Purchase #5 $176.62   4.236%   $184.1016   $184.10   $184.10   $184.10  
  Purchase #6 $234.30   13.770%   $266.5631   $266.56   $266.55   $266.60  
  Purchase #7 $73.87   5.356%   $77.8265   $77.83   $77.85   $77.80  
  7 purchase totals = $760.06       $828.7430   $828.75   $828.75   $828.80