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 $60.61   8.467%   $65.7418   $65.74   $65.75   $65.70  
  Purchase #2 $163.77   13.581%   $186.0116   $186.01   $186.00   $186.00  
  Purchase #3 $230.44   5.297%   $242.6464   $242.65   $242.65   $242.60  
  Purchase #4 $186.39   13.252%   $211.0904   $211.09   $211.10   $211.10  
  Purchase #5 $44.76   9.301%   $48.9231   $48.92   $48.90   $48.90  
  Purchase #6 $227.96   6.551%   $242.8937   $242.89   $242.90   $242.90  
  Purchase #7 $132.86   10.790%   $147.1956   $147.20   $147.20   $147.20  
  7 purchase totals = $1,046.79       $1,144.5026   $1,144.50   $1,144.50   $1,144.40