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 $125.61   8.749%   $136.5996   $136.60   $136.60   $136.60  
  Purchase #2 $171.53   7.714%   $184.7618   $184.76   $184.75   $184.80  
  Purchase #3 $26.82   9.184%   $29.2831   $29.28   $29.30   $29.30  
  Purchase #4 $5.53   11.249%   $6.1521   $6.15   $6.15   $6.20  
  Purchase #5 $225.68   3.120%   $232.7212   $232.72   $232.70   $232.70  
  Purchase #6 $50.81   5.327%   $53.5166   $53.52   $53.50   $53.50  
  Purchase #7 $231.51   10.246%   $255.2305   $255.23   $255.25   $255.20  
  7 purchase totals = $837.49       $898.2649   $898.26   $898.25   $898.30