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 $89.26   5.293%   $93.9845   $93.98   $94.00   $94.00  
  Purchase #2 $36.25   4.232%   $37.7841   $37.78   $37.80   $37.80  
  Purchase #3 $200.88   3.186%   $207.28   $207.28   $207.30   $207.30  
  Purchase #4 $191.75   3.711%   $198.8658   $198.87   $198.85   $198.90  
  Purchase #5 $52.94   4.399%   $55.2688   $55.27   $55.25   $55.30  
  Purchase #6 $13.40   10.487%   $14.8053   $14.81   $14.80   $14.80  
  Purchase #7 $216.38   10.337%   $238.7472   $238.75   $238.75   $238.70  
  7 purchase totals = $800.86       $846.7357   $846.74   $846.75   $846.80