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 $153.93   7.232%   $165.0622   $165.06   $165.05   $165.10  
  Purchase #2 $23.33   11.230%   $25.95   $25.95   $25.95   $26.00  
  Purchase #3 $24.55   10.295%   $27.0774   $27.08   $27.10   $27.10  
  Purchase #4 $159.97   7.145%   $171.3999   $171.40   $171.40   $171.40  
  Purchase #5 $74.54   10.308%   $82.2236   $82.22   $82.20   $82.20  
  Purchase #6 $63.99   10.537%   $70.7326   $70.73   $70.75   $70.70  
  Purchase #7 $175.37   5.729%   $185.4169   $185.42   $185.40   $185.40  
  7 purchase totals = $675.68       $727.8626   $727.86   $727.85   $727.90