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 $165.26   9.722%   $181.3266   $181.33   $181.35   $181.30  
  Purchase #2 $55.25   10.767%   $61.1988   $61.20   $61.20   $61.20  
  Purchase #3 $185.82   8.381%   $201.3936   $201.39   $201.40   $201.40  
  Purchase #4 $199.29   13.246%   $225.688   $225.69   $225.70   $225.70  
  Purchase #5 $206.66   4.707%   $216.3875   $216.39   $216.40   $216.40  
  Purchase #6 $41.99   9.847%   $46.1248   $46.12   $46.10   $46.10  
  Purchase #7 $17.67   4.708%   $18.5019   $18.50   $18.50   $18.50  
  7 purchase totals = $871.94       $950.6212   $950.62   $950.65   $950.60