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 $53.30   6.476%   $56.7517   $56.75   $56.75   $56.80  
  Purchase #2 $187.69   10.633%   $207.6471   $207.65   $207.65   $207.60  
  Purchase #3 $161.39   3.421%   $166.9112   $166.91   $166.90   $166.90  
  Purchase #4 $227.55   10.778%   $252.0753   $252.08   $252.10   $252.10  
  Purchase #5 $10.84   8.137%   $11.7221   $11.72   $11.70   $11.70  
  Purchase #6 $108.30   5.455%   $114.2078   $114.21   $114.20   $114.20  
  Purchase #7 $228.76   10.443%   $252.6494   $252.65   $252.65   $252.60  
  7 purchase totals = $977.83       $1,061.9646   $1,061.97   $1,061.95   $1,061.90