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 $240.39   9.283%   $262.7054   $262.71   $262.70   $262.70  
  Purchase #2 $236.32   11.132%   $262.6271   $262.63   $262.65   $262.60  
  Purchase #3 $155.40   9.669%   $170.4256   $170.43   $170.45   $170.40  
  Purchase #4 $60.49   6.279%   $64.2882   $64.29   $64.30   $64.30  
  Purchase #5 $106.83   6.122%   $113.3701   $113.37   $113.35   $113.40  
  Purchase #6 $241.48   10.273%   $266.2872   $266.29   $266.30   $266.30  
  Purchase #7 $113.41   11.194%   $126.1051   $126.11   $126.10   $126.10  
  7 purchase totals = $1,154.32       $1,265.8087   $1,265.83   $1,265.85   $1,265.80