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 $22.31   7.159%   $23.9072   $23.91   $23.90   $23.90  
  Purchase #2 $23.80   7.814%   $25.6597   $25.66   $25.65   $25.70  
  Purchase #3 $17.70   4.310%   $18.4629   $18.46   $18.45   $18.50  
  Purchase #4 $168.41   12.679%   $189.7627   $189.76   $189.75   $189.80  
  Purchase #5 $43.77   9.633%   $47.9864   $47.99   $48.00   $48.00  
  Purchase #6 $228.61   3.731%   $237.1394   $237.14   $237.15   $237.10  
  Purchase #7 $140.98   3.589%   $146.0398   $146.04   $146.05   $146.00  
  7 purchase totals = $645.58       $688.9581   $688.96   $688.95   $689.00