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 $52.57   12.247%   $59.0082   $59.01   $59.00   $59.00  
  Purchase #2 $35.81   4.288%   $37.3455   $37.35   $37.35   $37.30  
  Purchase #3 $27.68   8.662%   $30.0776   $30.08   $30.10   $30.10  
  Purchase #4 $248.28   3.729%   $257.5384   $257.54   $257.55   $257.50  
  Purchase #5 $210.69   5.108%   $221.452   $221.45   $221.45   $221.50  
  Purchase #6 $236.25   3.546%   $244.6274   $244.63   $244.65   $244.60  
  Purchase #7 $139.93   11.401%   $155.8834   $155.88   $155.90   $155.90  
  7 purchase totals = $951.21       $1,005.9325   $1,005.94   $1,006.00   $1,005.90