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 $230.82   7.215%   $247.4737   $247.47   $247.45   $247.50  
  Purchase #2 $221.82   3.195%   $228.9071   $228.91   $228.90   $228.90  
  Purchase #3 $165.63   8.573%   $179.8295   $179.83   $179.85   $179.80  
  Purchase #4 $132.44   12.359%   $148.8083   $148.81   $148.80   $148.80  
  Purchase #5 $147.27   7.217%   $157.8985   $157.90   $157.90   $157.90  
  Purchase #6 $77.75   13.847%   $88.516   $88.52   $88.50   $88.50  
  Purchase #7 $142.58   12.236%   $160.0261   $160.03   $160.05   $160.00  
  7 purchase totals = $1,118.31       $1,211.4592   $1,211.47   $1,211.45   $1,211.40