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 $166.76   10.854%   $184.8601   $184.86   $184.85   $184.90  
  Purchase #2 $217.65   12.176%   $244.1511   $244.15   $244.15   $244.20  
  Purchase #3 $20.30   11.786%   $22.6926   $22.69   $22.70   $22.70  
  Purchase #4 $202.32   11.183%   $224.9454   $224.95   $224.95   $224.90  
  Purchase #5 $179.30   6.150%   $190.327   $190.33   $190.35   $190.30  
  Purchase #6 $231.94   11.771%   $259.2417   $259.24   $259.25   $259.20  
  Purchase #7 $8.47   8.836%   $9.2184   $9.22   $9.20   $9.20  
  7 purchase totals = $1,026.74       $1,135.4363   $1,135.44   $1,135.45   $1,135.40