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 $49.76   13.583%   $56.5189   $56.52   $56.50   $56.50  
  Purchase #2 $214.62   12.550%   $241.5548   $241.55   $241.55   $241.60  
  Purchase #3 $5.48   8.294%   $5.9345   $5.93   $5.95   $5.90  
  Purchase #4 $30.54   9.490%   $33.4382   $33.44   $33.45   $33.40  
  Purchase #5 $19.75   12.243%   $22.168   $22.17   $22.15   $22.20  
  Purchase #6 $198.53   5.656%   $209.7589   $209.76   $209.75   $209.80  
  Purchase #7 $22.26   12.723%   $25.0921   $25.09   $25.10   $25.10  
  7 purchase totals = $540.94       $594.4654   $594.46   $594.45   $594.50