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 $245.96   9.616%   $269.6115   $269.61   $269.60   $269.60  
  Purchase #2 $184.57   12.678%   $207.9698   $207.97   $207.95   $208.00  
  Purchase #3 $117.69   8.709%   $127.9396   $127.94   $127.95   $127.90  
  Purchase #4 $230.35   5.480%   $242.9732   $242.97   $242.95   $243.00  
  Purchase #5 $219.97   4.621%   $230.1348   $230.13   $230.15   $230.10  
  Purchase #6 $220.51   4.303%   $229.9985   $230.00   $230.00   $230.00  
  Purchase #7 $246.51   3.780%   $255.8281   $255.83   $255.85   $255.80  
  7 purchase totals = $1,465.56       $1,564.4555   $1,564.45   $1,564.45   $1,564.40