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 $53.56   8.198%   $57.9508   $57.95   $57.95   $58.00  
  Purchase #2 $24.75   8.314%   $26.8077   $26.81   $26.80   $26.80  
  Purchase #3 $10.68   7.741%   $11.5067   $11.51   $11.50   $11.50  
  Purchase #4 $217.72   10.552%   $240.6938   $240.69   $240.70   $240.70  
  Purchase #5 $56.62   8.405%   $61.3789   $61.38   $61.40   $61.40  
  Purchase #6 $28.54   11.450%   $31.8078   $31.81   $31.80   $31.80  
  Purchase #7 $213.34   13.260%   $241.6289   $241.63   $241.65   $241.60  
  7 purchase totals = $605.21       $671.7746   $671.78   $671.80   $671.80