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 $98.59   12.865%   $111.2736   $111.27   $111.25   $111.30  
  Purchase #2 $176.42   11.847%   $197.3205   $197.32   $197.30   $197.30  
  Purchase #3 $56.78   8.378%   $61.537   $61.54   $61.55   $61.50  
  Purchase #4 $74.45   13.868%   $84.7747   $84.77   $84.75   $84.80  
  Purchase #5 $5.48   7.470%   $5.8894   $5.89   $5.90   $5.90  
  Purchase #6 $210.40   11.584%   $234.7727   $234.77   $234.75   $234.80  
  Purchase #7 $73.56   9.745%   $80.7284   $80.73   $80.75   $80.70  
  7 purchase totals = $695.68       $776.2963   $776.29   $776.25   $776.30