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 $246.37   11.119%   $273.7639   $273.76   $273.75   $273.80  
  Purchase #2 $154.27   5.768%   $163.1683   $163.17   $163.15   $163.20  
  Purchase #3 $138.99   9.626%   $152.3692   $152.37   $152.35   $152.40  
  Purchase #4 $9.58   11.483%   $10.6801   $10.68   $10.70   $10.70  
  Purchase #5 $122.80   9.647%   $134.6465   $134.65   $134.65   $134.60  
  Purchase #6 $233.47   3.355%   $241.3029   $241.30   $241.30   $241.30  
  Purchase #7 $111.56   4.865%   $116.9874   $116.99   $117.00   $117.00  
  7 purchase totals = $1,017.04       $1,092.9183   $1,092.92   $1,092.90   $1,093.00