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 $57.61   10.396%   $63.5991   $63.60   $63.60   $63.60  
  Purchase #2 $245.46   10.713%   $271.7561   $271.76   $271.75   $271.80  
  Purchase #3 $33.72   13.237%   $38.1835   $38.18   $38.20   $38.20  
  Purchase #4 $212.68   10.493%   $234.9965   $235.00   $235.00   $235.00  
  Purchase #5 $26.96   8.444%   $29.2365   $29.24   $29.25   $29.20  
  Purchase #6 $214.98   5.827%   $227.5069   $227.51   $227.50   $227.50  
  Purchase #7 $236.42   8.449%   $256.3951   $256.40   $256.40   $256.40  
  7 purchase totals = $1,027.83       $1,121.6737   $1,121.69   $1,121.70   $1,121.70