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 $52.85   12.205%   $59.3003   $59.30   $59.30   $59.30  
  Purchase #2 $33.42   11.517%   $37.269   $37.27   $37.25   $37.30  
  Purchase #3 $176.95   8.193%   $191.4475   $191.45   $191.45   $191.40  
  Purchase #4 $245.95   9.161%   $268.4815   $268.48   $268.50   $268.50  
  Purchase #5 $115.93   5.412%   $122.2041   $122.20   $122.20   $122.20  
  Purchase #6 $66.57   10.410%   $73.4999   $73.50   $73.50   $73.50  
  Purchase #7 $226.26   11.790%   $252.9361   $252.94   $252.95   $252.90  
  7 purchase totals = $917.93       $1,005.1384   $1,005.14   $1,005.15   $1,005.10