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 $184.78   13.229%   $209.2245   $209.22   $209.20   $209.20  
  Purchase #2 $172.30   4.245%   $179.6141   $179.61   $179.60   $179.60  
  Purchase #3 $195.35   5.147%   $205.4047   $205.40   $205.40   $205.40  
  Purchase #4 $55.65   11.325%   $61.9524   $61.95   $61.95   $62.00  
  Purchase #5 $224.40   3.353%   $231.9241   $231.92   $231.90   $231.90  
  Purchase #6 $209.85   11.841%   $234.6983   $234.70   $234.70   $234.70  
  Purchase #7 $163.30   6.336%   $173.6467   $173.65   $173.65   $173.60  
  7 purchase totals = $1,205.63       $1,296.4648   $1,296.45   $1,296.40   $1,296.40