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 $152.92   10.518%   $169.0041   $169.00   $169.00   $169.00  
  Purchase #2 $53.92   7.134%   $57.7667   $57.77   $57.75   $57.80  
  Purchase #3 $168.82   11.440%   $188.133   $188.13   $188.15   $188.10  
  Purchase #4 $56.36   13.509%   $63.9737   $63.97   $63.95   $64.00  
  Purchase #5 $166.90   12.829%   $188.3116   $188.31   $188.30   $188.30  
  Purchase #6 $205.38   5.156%   $215.9694   $215.97   $215.95   $216.00  
  Purchase #7 $138.92   11.659%   $155.1167   $155.12   $155.10   $155.10  
  7 purchase totals = $943.22       $1,038.2752   $1,038.27   $1,038.20   $1,038.30