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 $67.64   12.743%   $76.2594   $76.26   $76.25   $76.30  
  Purchase #2 $141.93   8.517%   $154.0182   $154.02   $154.00   $154.00  
  Purchase #3 $52.59   9.802%   $57.7449   $57.74   $57.75   $57.70  
  Purchase #4 $98.52   9.288%   $107.6705   $107.67   $107.65   $107.70  
  Purchase #5 $243.88   7.102%   $261.2004   $261.20   $261.20   $261.20  
  Purchase #6 $88.88   7.620%   $95.6527   $95.65   $95.65   $95.70  
  Purchase #7 $36.99   9.765%   $40.6021   $40.60   $40.60   $40.60  
  7 purchase totals = $730.43       $793.1482   $793.14   $793.10   $793.20