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 $241.48   4.859%   $253.2135   $253.21   $253.20   $253.20  
  Purchase #2 $135.58   12.211%   $152.1357   $152.14   $152.15   $152.10  
  Purchase #3 $115.91   9.107%   $126.4659   $126.47   $126.45   $126.50  
  Purchase #4 $26.78   12.860%   $30.2239   $30.22   $30.20   $30.20  
  Purchase #5 $190.54   11.488%   $212.4292   $212.43   $212.45   $212.40  
  Purchase #6 $233.46   10.154%   $257.1655   $257.17   $257.15   $257.20  
  Purchase #7 $181.59   13.603%   $206.2917   $206.29   $206.30   $206.30  
  7 purchase totals = $1,125.34       $1,237.9254   $1,237.93   $1,237.90   $1,237.90