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 $76.62   3.813%   $79.5415   $79.54   $79.55   $79.50  
  Purchase #2 $168.83   6.587%   $179.9508   $179.95   $179.95   $180.00  
  Purchase #3 $11.97   13.546%   $13.5915   $13.59   $13.60   $13.60  
  Purchase #4 $59.33   6.219%   $63.0197   $63.02   $63.00   $63.00  
  Purchase #5 $101.60   13.226%   $115.0376   $115.04   $115.05   $115.00  
  Purchase #6 $106.93   6.862%   $114.2675   $114.27   $114.25   $114.30  
  Purchase #7 $219.35   6.136%   $232.8093   $232.81   $232.80   $232.80  
  7 purchase totals = $744.63       $798.2179   $798.22   $798.20   $798.20