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 $228.85   8.658%   $248.6638   $248.66   $248.65   $248.70  
  Purchase #2 $29.25   12.178%   $32.8121   $32.81   $32.80   $32.80  
  Purchase #3 $183.58   6.439%   $195.4007   $195.40   $195.40   $195.40  
  Purchase #4 $87.36   5.225%   $91.9246   $91.92   $91.90   $91.90  
  Purchase #5 $165.96   12.149%   $186.1225   $186.12   $186.10   $186.10  
  Purchase #6 $135.64   8.123%   $146.658   $146.66   $146.65   $146.70  
  Purchase #7 $212.45   10.366%   $234.4726   $234.47   $234.45   $234.50  
  7 purchase totals = $1,043.09       $1,136.0543   $1,136.04   $1,135.95   $1,136.10