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 $215.25   12.851%   $242.9118   $242.91   $242.90   $242.90  
  Purchase #2 $184.50   11.443%   $205.6123   $205.61   $205.60   $205.60  
  Purchase #3 $63.59   5.292%   $66.9552   $66.96   $66.95   $67.00  
  Purchase #4 $116.81   4.758%   $122.3678   $122.37   $122.35   $122.40  
  Purchase #5 $234.86   3.183%   $242.3356   $242.34   $242.35   $242.30  
  Purchase #6 $52.68   7.638%   $56.7037   $56.70   $56.70   $56.70  
  Purchase #7 $232.46   11.756%   $259.788   $259.79   $259.80   $259.80  
  7 purchase totals = $1,100.15       $1,196.6744   $1,196.68   $1,196.65   $1,196.70