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 $22.42   8.171%   $24.2519   $24.25   $24.25   $24.30  
  Purchase #2 $182.65   10.579%   $201.9725   $201.97   $201.95   $202.00  
  Purchase #3 $15.45   3.199%   $15.9442   $15.94   $15.95   $15.90  
  Purchase #4 $142.72   9.238%   $155.9045   $155.90   $155.90   $155.90  
  Purchase #5 $25.96   5.522%   $27.3935   $27.39   $27.40   $27.40  
  Purchase #6 $138.73   9.611%   $152.0633   $152.06   $152.05   $152.10  
  Purchase #7 $167.65   9.190%   $183.057   $183.06   $183.05   $183.10  
  7 purchase totals = $695.58       $760.5869   $760.57   $760.55   $760.70