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 $58.55   4.782%   $61.3499   $61.35   $61.35   $61.30  
  Purchase #2 $222.79   4.519%   $232.8579   $232.86   $232.85   $232.90  
  Purchase #3 $118.95   4.285%   $124.047   $124.05   $124.05   $124.00  
  Purchase #4 $34.41   3.308%   $35.5483   $35.55   $35.55   $35.50  
  Purchase #5 $133.32   12.846%   $150.4463   $150.45   $150.45   $150.40  
  Purchase #6 $242.59   5.233%   $255.2847   $255.28   $255.30   $255.30  
  Purchase #7 $5.67   3.166%   $5.8495   $5.85   $5.85   $5.80  
  7 purchase totals = $816.28       $865.3836   $865.39   $865.40   $865.20