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 $238.56   11.633%   $266.3117   $266.31   $266.30   $266.30  
  Purchase #2 $226.50   8.476%   $245.6981   $245.70   $245.70   $245.70  
  Purchase #3 $54.65   12.551%   $61.5091   $61.51   $61.50   $61.50  
  Purchase #4 $222.36   3.109%   $229.2732   $229.27   $229.25   $229.30  
  Purchase #5 $152.30   6.222%   $161.7761   $161.78   $161.80   $161.80  
  Purchase #6 $173.54   5.263%   $182.6734   $182.67   $182.65   $182.70  
  Purchase #7 $9.58   8.474%   $10.3918   $10.39   $10.40   $10.40  
  7 purchase totals = $1,077.49       $1,157.6334   $1,157.63   $1,157.60   $1,157.70