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 $213.70   13.133%   $241.7652   $241.77   $241.75   $241.80  
  Purchase #2 $128.93   4.267%   $134.4314   $134.43   $134.45   $134.40  
  Purchase #3 $38.71   5.448%   $40.8189   $40.82   $40.80   $40.80  
  Purchase #4 $67.78   11.208%   $75.3768   $75.38   $75.40   $75.40  
  Purchase #5 $207.70   8.232%   $224.7979   $224.80   $224.80   $224.80  
  Purchase #6 $108.38   6.758%   $115.7043   $115.70   $115.70   $115.70  
  Purchase #7 $229.73   9.274%   $251.0352   $251.04   $251.05   $251.00  
  7 purchase totals = $994.93       $1,083.9297   $1,083.94   $1,083.95   $1,083.90