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 $209.32   11.773%   $233.9632   $233.96   $233.95   $234.00  
  Purchase #2 $134.69   12.246%   $151.1841   $151.18   $151.20   $151.20  
  Purchase #3 $35.29   12.380%   $39.6589   $39.66   $39.65   $39.70  
  Purchase #4 $15.54   12.303%   $17.4519   $17.45   $17.45   $17.50  
  Purchase #5 $134.69   5.236%   $141.7424   $141.74   $141.75   $141.70  
  Purchase #6 $206.73   9.794%   $226.9771   $226.98   $227.00   $227.00  
  Purchase #7 $226.80   9.644%   $248.6726   $248.67   $248.65   $248.70  
  7 purchase totals = $963.06       $1,059.6502   $1,059.64   $1,059.65   $1,059.80