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 $23.64   12.293%   $26.5461   $26.55   $26.55   $26.50  
  Purchase #2 $43.39   8.345%   $47.0109   $47.01   $47.00   $47.00  
  Purchase #3 $69.59   11.874%   $77.8531   $77.85   $77.85   $77.90  
  Purchase #4 $200.52   13.186%   $226.9606   $226.96   $226.95   $227.00  
  Purchase #5 $202.70   10.481%   $223.945   $223.95   $223.95   $223.90  
  Purchase #6 $233.49   12.696%   $263.1339   $263.13   $263.15   $263.10  
  Purchase #7 $31.26   6.530%   $33.3013   $33.30   $33.30   $33.30  
  7 purchase totals = $804.59       $898.7509   $898.75   $898.75   $898.70