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 $202.83   4.282%   $211.5152   $211.52   $211.50   $211.50  
  Purchase #2 $249.98   3.849%   $259.6017   $259.60   $259.60   $259.60  
  Purchase #3 $209.48   12.756%   $236.2013   $236.20   $236.20   $236.20  
  Purchase #4 $51.90   8.509%   $56.3162   $56.32   $56.30   $56.30  
  Purchase #5 $215.67   6.788%   $230.3097   $230.31   $230.30   $230.30  
  Purchase #6 $59.35   7.299%   $63.682   $63.68   $63.70   $63.70  
  Purchase #7 $210.80   6.337%   $224.1584   $224.16   $224.15   $224.20  
  7 purchase totals = $1,200.01       $1,281.7845   $1,281.79   $1,281.75   $1,281.80