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 $35.41   5.616%   $37.3986   $37.40   $37.40   $37.40  
  Purchase #2 $120.31   3.356%   $124.3476   $124.35   $124.35   $124.30  
  Purchase #3 $171.37   9.495%   $187.6416   $187.64   $187.65   $187.60  
  Purchase #4 $94.93   3.852%   $98.5867   $98.59   $98.60   $98.60  
  Purchase #5 $11.89   8.591%   $12.9115   $12.91   $12.90   $12.90  
  Purchase #6 $123.73   4.714%   $129.5626   $129.56   $129.55   $129.60  
  Purchase #7 $32.57   8.815%   $35.441   $35.44   $35.45   $35.40  
  7 purchase totals = $590.21       $625.8896   $625.89   $625.90   $625.80