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 $178.92   3.796%   $185.7118   $185.71   $185.70   $185.70  
  Purchase #2 $229.28   6.379%   $243.9058   $243.91   $243.90   $243.90  
  Purchase #3 $55.84   8.851%   $60.7824   $60.78   $60.80   $60.80  
  Purchase #4 $18.35   8.173%   $19.8497   $19.85   $19.85   $19.80  
  Purchase #5 $165.92   6.183%   $176.1788   $176.18   $176.20   $176.20  
  Purchase #6 $239.48   12.443%   $269.2785   $269.28   $269.30   $269.30  
  Purchase #7 $52.67   10.631%   $58.2693   $58.27   $58.25   $58.30  
  7 purchase totals = $940.46       $1,013.9763   $1,013.98   $1,014.00   $1,014.00