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 $52.66   6.515%   $56.0908   $56.09   $56.10   $56.10  
  Purchase #2 $232.60   6.107%   $246.8049   $246.80   $246.80   $246.80  
  Purchase #3 $159.48   4.473%   $166.6135   $166.61   $166.60   $166.60  
  Purchase #4 $104.83   4.251%   $109.2863   $109.29   $109.30   $109.30  
  Purchase #5 $236.67   9.676%   $259.5702   $259.57   $259.55   $259.60  
  Purchase #6 $86.46   10.660%   $95.6766   $95.68   $95.70   $95.70  
  Purchase #7 $139.29   6.163%   $147.8744   $147.87   $147.85   $147.90  
  7 purchase totals = $1,011.99       $1,081.9167   $1,081.91   $1,081.90   $1,082.00