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 $238.52   12.340%   $267.9534   $267.95   $267.95   $268.00  
  Purchase #2 $179.59   12.446%   $201.9418   $201.94   $201.95   $201.90  
  Purchase #3 $99.73   6.215%   $105.9282   $105.93   $105.95   $105.90  
  Purchase #4 $106.32   6.737%   $113.4828   $113.48   $113.50   $113.50  
  Purchase #5 $77.72   12.638%   $87.5423   $87.54   $87.55   $87.50  
  Purchase #6 $95.53   3.759%   $99.121   $99.12   $99.10   $99.10  
  Purchase #7 $46.99   6.822%   $50.1957   $50.20   $50.20   $50.20  
  7 purchase totals = $844.40       $926.1652   $926.16   $926.20   $926.10