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 $53.85   12.281%   $60.4633   $60.46   $60.45   $60.50  
  Purchase #2 $151.43   11.362%   $168.6355   $168.64   $168.65   $168.60  
  Purchase #3 $145.99   4.710%   $152.8661   $152.87   $152.85   $152.90  
  Purchase #4 $24.64   5.679%   $26.0393   $26.04   $26.05   $26.00  
  Purchase #5 $102.65   3.755%   $106.5045   $106.50   $106.50   $106.50  
  Purchase #6 $16.27   5.296%   $17.1317   $17.13   $17.15   $17.10  
  Purchase #7 $23.32   10.688%   $25.8124   $25.81   $25.80   $25.80  
  7 purchase totals = $518.15       $557.4528   $557.45   $557.45   $557.40