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 $93.26   12.626%   $105.035   $105.04   $105.05   $105.00  
  Purchase #2 $195.46   13.351%   $221.5559   $221.56   $221.55   $221.60  
  Purchase #3 $58.28   3.130%   $60.1042   $60.10   $60.10   $60.10  
  Purchase #4 $235.63   3.294%   $243.3917   $243.39   $243.40   $243.40  
  Purchase #5 $114.91   13.715%   $130.6699   $130.67   $130.65   $130.70  
  Purchase #6 $161.53   13.232%   $182.9036   $182.90   $182.90   $182.90  
  Purchase #7 $68.52   11.378%   $76.3162   $76.32   $76.30   $76.30  
  7 purchase totals = $927.59       $1,019.9765   $1,019.98   $1,019.95   $1,020.00