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 $115.27   4.336%   $120.2681   $120.27   $120.25   $120.30  
  Purchase #2 $175.45   7.753%   $189.0526   $189.05   $189.05   $189.10  
  Purchase #3 $139.25   8.255%   $150.7451   $150.75   $150.75   $150.70  
  Purchase #4 $131.46   3.598%   $136.1899   $136.19   $136.20   $136.20  
  Purchase #5 $208.95   10.550%   $230.9942   $230.99   $231.00   $231.00  
  Purchase #6 $237.50   9.335%   $259.6706   $259.67   $259.65   $259.70  
  Purchase #7 $11.31   7.132%   $12.1166   $12.12   $12.10   $12.10  
  7 purchase totals = $1,019.19       $1,099.0371   $1,099.04   $1,099.00   $1,099.10