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 $56.91   5.483%   $60.0304   $60.03   $60.05   $60.00  
  Purchase #2 $56.45   12.450%   $63.478   $63.48   $63.50   $63.50  
  Purchase #3 $168.41   3.714%   $174.6647   $174.66   $174.65   $174.70  
  Purchase #4 $126.32   9.283%   $138.0463   $138.05   $138.05   $138.00  
  Purchase #5 $121.96   13.155%   $138.0038   $138.00   $138.00   $138.00  
  Purchase #6 $146.47   4.547%   $153.13   $153.13   $153.15   $153.10  
  Purchase #7 $56.62   3.742%   $58.7387   $58.74   $58.75   $58.70  
  7 purchase totals = $733.14       $786.0919   $786.09   $786.15   $786.00