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 $248.54   3.817%   $258.0268   $258.03   $258.05   $258.00  
  Purchase #2 $205.50   4.840%   $215.4462   $215.45   $215.45   $215.40  
  Purchase #3 $55.27   13.234%   $62.5844   $62.58   $62.60   $62.60  
  Purchase #4 $22.54   9.743%   $24.7361   $24.74   $24.75   $24.70  
  Purchase #5 $168.71   5.540%   $178.0565   $178.06   $178.05   $178.10  
  Purchase #6 $166.92   12.422%   $187.6548   $187.65   $187.65   $187.70  
  Purchase #7 $127.40   4.384%   $132.9852   $132.99   $133.00   $133.00  
  7 purchase totals = $994.88       $1,059.4900   $1,059.50   $1,059.55   $1,059.50