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 $176.81   11.172%   $196.5632   $196.56   $196.55   $196.60  
  Purchase #2 $220.70   9.754%   $242.2271   $242.23   $242.25   $242.20  
  Purchase #3 $213.60   6.198%   $226.8389   $226.84   $226.85   $226.80  
  Purchase #4 $113.82   11.136%   $126.495   $126.50   $126.50   $126.50  
  Purchase #5 $102.44   6.332%   $108.9265   $108.93   $108.95   $108.90  
  Purchase #6 $244.72   3.332%   $252.8741   $252.87   $252.85   $252.90  
  Purchase #7 $24.70   10.622%   $27.3236   $27.32   $27.30   $27.30  
  7 purchase totals = $1,096.79       $1,181.2484   $1,181.25   $1,181.25   $1,181.20