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 $48.55   9.743%   $53.2802   $53.28   $53.30   $53.30  
  Purchase #2 $245.38   12.573%   $276.2316   $276.23   $276.25   $276.20  
  Purchase #3 $95.47   10.658%   $105.6452   $105.65   $105.65   $105.60  
  Purchase #4 $66.27   10.842%   $73.455   $73.46   $73.45   $73.50  
  Purchase #5 $221.69   6.430%   $235.9447   $235.94   $235.95   $235.90  
  Purchase #6 $119.79   12.116%   $134.3038   $134.30   $134.30   $134.30  
  Purchase #7 $188.70   10.386%   $208.2984   $208.30   $208.30   $208.30  
  7 purchase totals = $985.85       $1,087.1589   $1,087.16   $1,087.20   $1,087.10