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 $244.46   5.403%   $257.6682   $257.67   $257.65   $257.70  
  Purchase #2 $214.76   5.732%   $227.07   $227.07   $227.05   $227.10  
  Purchase #3 $186.92   8.436%   $202.6886   $202.69   $202.70   $202.70  
  Purchase #4 $87.96   10.280%   $97.0023   $97.00   $97.00   $97.00  
  Purchase #5 $227.57   8.372%   $246.6222   $246.62   $246.60   $246.60  
  Purchase #6 $42.42   3.291%   $43.816   $43.82   $43.80   $43.80  
  Purchase #7 $62.63   5.139%   $65.8486   $65.85   $65.85   $65.80  
  7 purchase totals = $1,066.72       $1,140.7159   $1,140.72   $1,140.65   $1,140.70