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 $89.25   13.456%   $101.2595   $101.26   $101.25   $101.30  
  Purchase #2 $97.62   11.209%   $108.5622   $108.56   $108.55   $108.60  
  Purchase #3 $31.74   11.132%   $35.2733   $35.27   $35.25   $35.30  
  Purchase #4 $82.83   12.773%   $93.4099   $93.41   $93.40   $93.40  
  Purchase #5 $185.59   6.344%   $197.3638   $197.36   $197.35   $197.40  
  Purchase #6 $236.72   4.284%   $246.8611   $246.86   $246.85   $246.90  
  Purchase #7 $212.98   4.627%   $222.8346   $222.83   $222.85   $222.80  
  7 purchase totals = $936.73       $1,005.5644   $1,005.55   $1,005.50   $1,005.70