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 $41.30   7.268%   $44.3017   $44.30   $44.30   $44.30  
  Purchase #2 $165.70   6.673%   $176.7572   $176.76   $176.75   $176.80  
  Purchase #3 $121.48   13.542%   $137.9308   $137.93   $137.95   $137.90  
  Purchase #4 $177.92   8.437%   $192.9311   $192.93   $192.95   $192.90  
  Purchase #5 $102.66   6.370%   $109.1994   $109.20   $109.20   $109.20  
  Purchase #6 $95.91   8.719%   $104.2724   $104.27   $104.25   $104.30  
  Purchase #7 $231.29   9.699%   $253.7228   $253.72   $253.70   $253.70  
  7 purchase totals = $936.26       $1,019.1154   $1,019.11   $1,019.10   $1,019.10