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 $243.40   10.725%   $269.5047   $269.50   $269.50   $269.50  
  Purchase #2 $115.47   6.401%   $122.8612   $122.86   $122.85   $122.90  
  Purchase #3 $34.40   10.449%   $37.9945   $37.99   $38.00   $38.00  
  Purchase #4 $53.85   12.134%   $60.3842   $60.38   $60.40   $60.40  
  Purchase #5 $166.68   8.250%   $180.4311   $180.43   $180.45   $180.40  
  Purchase #6 $141.42   11.178%   $157.2279   $157.23   $157.25   $157.20  
  Purchase #7 $224.54   3.405%   $232.1856   $232.19   $232.20   $232.20  
  7 purchase totals = $979.76       $1,060.5892   $1,060.58   $1,060.65   $1,060.60