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 $33.86   5.299%   $35.6542   $35.65   $35.65   $35.70  
  Purchase #2 $115.74   13.233%   $131.0559   $131.06   $131.05   $131.10  
  Purchase #3 $45.99   10.634%   $50.8806   $50.88   $50.90   $50.90  
  Purchase #4 $222.34   5.681%   $234.9711   $234.97   $234.95   $235.00  
  Purchase #5 $124.93   12.648%   $140.7311   $140.73   $140.75   $140.70  
  Purchase #6 $121.90   12.408%   $137.0254   $137.03   $137.05   $137.00  
  Purchase #7 $34.28   7.294%   $36.7804   $36.78   $36.80   $36.80  
  7 purchase totals = $699.04       $767.0987   $767.10   $767.15   $767.20