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 $68.55   12.824%   $77.3409   $77.34   $77.35   $77.30  
  Purchase #2 $195.36   11.801%   $218.4144   $218.41   $218.40   $218.40  
  Purchase #3 $157.32   3.777%   $163.262   $163.26   $163.25   $163.30  
  Purchase #4 $186.36   13.518%   $211.5521   $211.55   $211.55   $211.60  
  Purchase #5 $38.64   13.221%   $43.7486   $43.75   $43.75   $43.70  
  Purchase #6 $10.94   7.518%   $11.7625   $11.76   $11.75   $11.80  
  Purchase #7 $24.38   7.859%   $26.296   $26.30   $26.30   $26.30  
  7 purchase totals = $681.55       $752.3765   $752.37   $752.35   $752.40