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 $226.65   13.615%   $257.5084   $257.51   $257.50   $257.50  
  Purchase #2 $178.68   8.435%   $193.7517   $193.75   $193.75   $193.80  
  Purchase #3 $111.45   3.643%   $115.5101   $115.51   $115.50   $115.50  
  Purchase #4 $241.89   10.777%   $267.9585   $267.96   $267.95   $268.00  
  Purchase #5 $83.80   3.627%   $86.8394   $86.84   $86.85   $86.80  
  Purchase #6 $45.62   12.409%   $51.281   $51.28   $51.30   $51.30  
  Purchase #7 $82.43   6.413%   $87.7162   $87.72   $87.70   $87.70  
  7 purchase totals = $970.52       $1,060.5653   $1,060.57   $1,060.55   $1,060.60