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 $53.80   8.635%   $58.4456   $58.45   $58.45   $58.40  
  Purchase #2 $232.40   7.445%   $249.7022   $249.70   $249.70   $249.70  
  Purchase #3 $8.75   5.110%   $9.1971   $9.20   $9.20   $9.20  
  Purchase #4 $222.88   11.825%   $249.2356   $249.24   $249.25   $249.20  
  Purchase #5 $68.29   12.728%   $76.982   $76.98   $77.00   $77.00  
  Purchase #6 $62.83   4.544%   $65.685   $65.69   $65.70   $65.70  
  Purchase #7 $179.86   5.843%   $190.3692   $190.37   $190.35   $190.40  
  7 purchase totals = $828.81       $899.6167   $899.63   $899.65   $899.60