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 $192.52   4.247%   $200.6963   $200.70   $200.70   $200.70  
  Purchase #2 $44.36   5.356%   $46.7359   $46.74   $46.75   $46.70  
  Purchase #3 $246.85   10.694%   $273.2481   $273.25   $273.25   $273.20  
  Purchase #4 $59.43   11.617%   $66.334   $66.33   $66.35   $66.30  
  Purchase #5 $113.44   12.418%   $127.527   $127.53   $127.55   $127.50  
  Purchase #6 $136.67   7.616%   $147.0788   $147.08   $147.10   $147.10  
  Purchase #7 $117.74   6.583%   $125.4908   $125.49   $125.50   $125.50  
  7 purchase totals = $911.01       $987.1109   $987.12   $987.20   $987.00