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 $38.95   11.336%   $43.3654   $43.37   $43.35   $43.40  
  Purchase #2 $163.54   12.465%   $183.9253   $183.93   $183.95   $183.90  
  Purchase #3 $135.91   12.269%   $152.5848   $152.58   $152.60   $152.60  
  Purchase #4 $207.46   9.248%   $226.6459   $226.65   $226.65   $226.60  
  Purchase #5 $145.66   12.866%   $164.4006   $164.40   $164.40   $164.40  
  Purchase #6 $203.43   3.336%   $210.2164   $210.22   $210.20   $210.20  
  Purchase #7 $166.49   12.623%   $187.506   $187.51   $187.50   $187.50  
  7 purchase totals = $1,061.44       $1,168.6444   $1,168.66   $1,168.65   $1,168.60