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 $58.33   6.533%   $62.1407   $62.14   $62.15   $62.10  
  Purchase #2 $137.99   12.773%   $155.6155   $155.62   $155.60   $155.60  
  Purchase #3 $54.35   5.674%   $57.4338   $57.43   $57.45   $57.40  
  Purchase #4 $166.68   8.716%   $181.2078   $181.21   $181.20   $181.20  
  Purchase #5 $169.59   12.792%   $191.284   $191.28   $191.30   $191.30  
  Purchase #6 $89.43   4.386%   $93.3524   $93.35   $93.35   $93.40  
  Purchase #7 $106.77   11.691%   $119.2525   $119.25   $119.25   $119.30  
  7 purchase totals = $783.14       $860.2867   $860.28   $860.30   $860.30