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 $44.48   11.166%   $49.4466   $49.45   $49.45   $49.40  
  Purchase #2 $163.87   7.241%   $175.7358   $175.74   $175.75   $175.70  
  Purchase #3 $110.51   11.743%   $123.4872   $123.49   $123.50   $123.50  
  Purchase #4 $241.53   6.206%   $256.5194   $256.52   $256.50   $256.50  
  Purchase #5 $63.85   11.519%   $71.2049   $71.20   $71.20   $71.20  
  Purchase #6 $247.80   10.866%   $274.7259   $274.73   $274.75   $274.70  
  Purchase #7 $130.70   13.497%   $148.3406   $148.34   $148.35   $148.30  
  7 purchase totals = $1,002.74       $1,099.4604   $1,099.47   $1,099.50   $1,099.30