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 $232.60   4.441%   $242.9298   $242.93   $242.95   $242.90  
  Purchase #2 $72.79   5.754%   $76.9783   $76.98   $77.00   $77.00  
  Purchase #3 $241.45   5.446%   $254.5994   $254.60   $254.60   $254.60  
  Purchase #4 $151.61   3.742%   $157.2832   $157.28   $157.30   $157.30  
  Purchase #5 $157.41   10.801%   $174.4119   $174.41   $174.40   $174.40  
  Purchase #6 $65.35   12.803%   $73.7168   $73.72   $73.70   $73.70  
  Purchase #7 $62.96   11.114%   $69.9574   $69.96   $69.95   $70.00  
  7 purchase totals = $984.17       $1,049.8768   $1,049.88   $1,049.90   $1,049.90