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 $241.92   10.263%   $266.7482   $266.75   $266.75   $266.70  
  Purchase #2 $226.98   10.640%   $251.1307   $251.13   $251.15   $251.10  
  Purchase #3 $33.68   6.840%   $35.9837   $35.98   $36.00   $36.00  
  Purchase #4 $236.72   3.512%   $245.0336   $245.03   $245.05   $245.00  
  Purchase #5 $245.29   11.777%   $274.1778   $274.18   $274.20   $274.20  
  Purchase #6 $243.61   6.651%   $259.8125   $259.81   $259.80   $259.80  
  Purchase #7 $102.83   5.176%   $108.1525   $108.15   $108.15   $108.20  
  7 purchase totals = $1,331.03       $1,441.0390   $1,441.03   $1,441.10   $1,441.00