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 $23.82   9.724%   $26.1363   $26.14   $26.15   $26.10  
  Purchase #2 $47.47   4.453%   $49.5838   $49.58   $49.60   $49.60  
  Purchase #3 $119.34   6.301%   $126.8596   $126.86   $126.85   $126.90  
  Purchase #4 $206.71   12.771%   $233.1089   $233.11   $233.10   $233.10  
  Purchase #5 $105.43   13.498%   $119.6609   $119.66   $119.65   $119.70  
  Purchase #6 $247.85   8.239%   $268.2704   $268.27   $268.25   $268.30  
  Purchase #7 $96.87   10.735%   $107.269   $107.27   $107.25   $107.30  
  7 purchase totals = $847.49       $930.8889   $930.89   $930.85   $931.00