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 $70.56   5.671%   $74.5615   $74.56   $74.55   $74.60  
  Purchase #2 $243.54   11.559%   $271.6908   $271.69   $271.70   $271.70  
  Purchase #3 $64.37   6.621%   $68.6319   $68.63   $68.65   $68.60  
  Purchase #4 $239.61   4.158%   $249.573   $249.57   $249.55   $249.60  
  Purchase #5 $34.43   11.611%   $38.4277   $38.43   $38.45   $38.40  
  Purchase #6 $197.94   5.556%   $208.9375   $208.94   $208.95   $208.90  
  Purchase #7 $88.86   11.510%   $99.0878   $99.09   $99.10   $99.10  
  7 purchase totals = $939.31       $1,010.9102   $1,010.91   $1,010.95   $1,010.90