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 $60.65   12.256%   $68.0833   $68.08   $68.10   $68.10  
  Purchase #2 $158.72   6.533%   $169.0892   $169.09   $169.10   $169.10  
  Purchase #3 $200.40   8.370%   $217.1735   $217.17   $217.15   $217.20  
  Purchase #4 $189.75   4.654%   $198.581   $198.58   $198.60   $198.60  
  Purchase #5 $138.80   12.396%   $156.0056   $156.01   $156.00   $156.00  
  Purchase #6 $250.61   8.522%   $271.967   $271.97   $271.95   $272.00  
  Purchase #7 $90.45   12.687%   $101.9254   $101.93   $101.95   $101.90  
  7 purchase totals = $1,089.38       $1,182.8250   $1,182.83   $1,182.85   $1,182.90