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 $79.52   8.111%   $85.9699   $85.97   $85.95   $86.00  
  Purchase #2 $132.86   8.339%   $143.9392   $143.94   $143.95   $143.90  
  Purchase #3 $205.86   7.393%   $221.0792   $221.08   $221.10   $221.10  
  Purchase #4 $166.31   8.281%   $180.0821   $180.08   $180.10   $180.10  
  Purchase #5 $53.83   8.229%   $58.2597   $58.26   $58.25   $58.30  
  Purchase #6 $114.48   7.730%   $123.3293   $123.33   $123.35   $123.30  
  Purchase #7 $9.27   9.391%   $10.1405   $10.14   $10.15   $10.10  
  7 purchase totals = $762.13       $822.7999   $822.80   $822.85   $822.80