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 $225.39   6.784%   $240.6805   $240.68   $240.70   $240.70  
  Purchase #2 $211.33   11.619%   $235.8844   $235.88   $235.90   $235.90  
  Purchase #3 $217.75   4.169%   $226.828   $226.83   $226.85   $226.80  
  Purchase #4 $49.41   3.304%   $51.0425   $51.04   $51.05   $51.00  
  Purchase #5 $60.38   5.349%   $63.6097   $63.61   $63.60   $63.60  
  Purchase #6 $124.44   9.584%   $136.3663   $136.37   $136.35   $136.40  
  Purchase #7 $76.87   7.153%   $82.3685   $82.37   $82.35   $82.40  
  7 purchase totals = $965.57       $1,036.7799   $1,036.78   $1,036.80   $1,036.80