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 $88.32   8.779%   $96.0736   $96.07   $96.05   $96.10  
  Purchase #2 $208.43   9.150%   $227.5013   $227.50   $227.50   $227.50  
  Purchase #3 $9.69   11.473%   $10.8017   $10.80   $10.80   $10.80  
  Purchase #4 $52.60   5.851%   $55.6776   $55.68   $55.70   $55.70  
  Purchase #5 $160.40   13.845%   $182.6074   $182.61   $182.60   $182.60  
  Purchase #6 $48.46   8.687%   $52.6697   $52.67   $52.65   $52.70  
  Purchase #7 $193.57   9.210%   $211.3978   $211.40   $211.40   $211.40  
  7 purchase totals = $761.47       $836.7291   $836.73   $836.70   $836.80