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 $142.47   5.116%   $149.7588   $149.76   $149.75   $149.80  
  Purchase #2 $204.60   11.853%   $228.8512   $228.85   $228.85   $228.90  
  Purchase #3 $121.92   10.657%   $134.913   $134.91   $134.90   $134.90  
  Purchase #4 $24.55   5.782%   $25.9695   $25.97   $25.95   $26.00  
  Purchase #5 $94.57   10.575%   $104.5708   $104.57   $104.55   $104.60  
  Purchase #6 $215.32   5.419%   $226.9882   $226.99   $227.00   $227.00  
  Purchase #7 $250.62   13.539%   $284.5514   $284.55   $284.55   $284.60  
  7 purchase totals = $1,054.05       $1,155.6029   $1,155.60   $1,155.55   $1,155.80