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 $56.53   10.125%   $62.2537   $62.25   $62.25   $62.30  
  Purchase #2 $123.86   12.652%   $139.5308   $139.53   $139.55   $139.50  
  Purchase #3 $196.64   7.434%   $211.2582   $211.26   $211.25   $211.30  
  Purchase #4 $215.48   6.129%   $228.6868   $228.69   $228.70   $228.70  
  Purchase #5 $95.67   6.255%   $101.6542   $101.65   $101.65   $101.70  
  Purchase #6 $165.61   13.284%   $187.6096   $187.61   $187.60   $187.60  
  Purchase #7 $74.78   7.461%   $80.3593   $80.36   $80.35   $80.40  
  7 purchase totals = $928.57       $1,011.3526   $1,011.35   $1,011.35   $1,011.50