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 $58.89   13.779%   $67.0045   $67.00   $67.00   $67.00  
  Purchase #2 $48.80   10.684%   $54.0138   $54.01   $54.00   $54.00  
  Purchase #3 $168.29   9.155%   $183.6969   $183.70   $183.70   $183.70  
  Purchase #4 $208.95   11.521%   $233.0231   $233.02   $233.00   $233.00  
  Purchase #5 $140.33   8.582%   $152.3731   $152.37   $152.35   $152.40  
  Purchase #6 $57.40   11.762%   $64.1514   $64.15   $64.15   $64.20  
  Purchase #7 $41.97   8.298%   $45.4527   $45.45   $45.45   $45.50  
  7 purchase totals = $724.63       $799.7155   $799.70   $799.65   $799.80