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 $49.82   7.520%   $53.5665   $53.57   $53.55   $53.60  
  Purchase #2 $53.91   12.302%   $60.542   $60.54   $60.55   $60.50  
  Purchase #3 $166.75   12.147%   $187.0051   $187.01   $187.00   $187.00  
  Purchase #4 $234.47   6.239%   $249.0986   $249.10   $249.10   $249.10  
  Purchase #5 $142.39   8.804%   $154.926   $154.93   $154.95   $154.90  
  Purchase #6 $171.94   6.418%   $182.9751   $182.98   $183.00   $183.00  
  Purchase #7 $115.72   6.309%   $123.0208   $123.02   $123.00   $123.00  
  7 purchase totals = $935.00       $1,011.1341   $1,011.15   $1,011.15   $1,011.10