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 $56.58   8.402%   $61.3339   $61.33   $61.35   $61.30  
  Purchase #2 $160.37   3.354%   $165.7488   $165.75   $165.75   $165.70  
  Purchase #3 $33.47   10.448%   $36.9669   $36.97   $36.95   $37.00  
  Purchase #4 $206.99   10.431%   $228.5811   $228.58   $228.60   $228.60  
  Purchase #5 $19.36   7.722%   $20.855   $20.86   $20.85   $20.90  
  Purchase #6 $74.53   13.782%   $84.8017   $84.80   $84.80   $84.80  
  Purchase #7 $72.57   11.521%   $80.9308   $80.93   $80.95   $80.90  
  7 purchase totals = $623.87       $679.2182   $679.22   $679.25   $679.20