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 $108.56   6.412%   $115.5209   $115.52   $115.50   $115.50  
  Purchase #2 $236.91   10.803%   $262.5034   $262.50   $262.50   $262.50  
  Purchase #3 $75.76   9.164%   $82.7026   $82.70   $82.70   $82.70  
  Purchase #4 $38.55   7.177%   $41.3167   $41.32   $41.30   $41.30  
  Purchase #5 $52.32   11.699%   $58.4409   $58.44   $58.45   $58.40  
  Purchase #6 $54.25   8.637%   $58.9356   $58.94   $58.95   $58.90  
  Purchase #7 $246.89   7.817%   $266.1894   $266.19   $266.20   $266.20  
  7 purchase totals = $813.24       $885.6095   $885.61   $885.60   $885.50