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 $92.73   6.286%   $98.559   $98.56   $98.55   $98.60  
  Purchase #2 $232.99   9.635%   $255.4386   $255.44   $255.45   $255.40  
  Purchase #3 $8.75   9.178%   $9.5531   $9.55   $9.55   $9.60  
  Purchase #4 $193.83   8.607%   $210.5129   $210.51   $210.50   $210.50  
  Purchase #5 $126.53   10.112%   $139.3247   $139.32   $139.30   $139.30  
  Purchase #6 $101.35   5.633%   $107.059   $107.06   $107.05   $107.10  
  Purchase #7 $49.91   13.605%   $56.7003   $56.70   $56.70   $56.70  
  7 purchase totals = $806.09       $877.1476   $877.14   $877.10   $877.20