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 $174.86   11.109%   $194.2852   $194.29   $194.30   $194.30  
  Purchase #2 $247.67   3.632%   $256.6654   $256.67   $256.65   $256.70  
  Purchase #3 $199.93   8.705%   $217.3339   $217.33   $217.35   $217.30  
  Purchase #4 $127.61   13.702%   $145.0951   $145.10   $145.10   $145.10  
  Purchase #5 $192.26   12.307%   $215.9214   $215.92   $215.90   $215.90  
  Purchase #6 $21.92   8.268%   $23.7323   $23.73   $23.75   $23.70  
  Purchase #7 $154.66   11.224%   $172.019   $172.02   $172.00   $172.00  
  7 purchase totals = $1,118.91       $1,225.0523   $1,225.06   $1,225.05   $1,225.00