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 $61.57   7.627%   $66.2659   $66.27   $66.25   $66.30  
  Purchase #2 $198.86   6.461%   $211.7083   $211.71   $211.70   $211.70  
  Purchase #3 $223.88   4.705%   $234.4136   $234.41   $234.40   $234.40  
  Purchase #4 $110.55   11.431%   $123.187   $123.19   $123.20   $123.20  
  Purchase #5 $161.70   12.544%   $181.9836   $181.98   $182.00   $182.00  
  Purchase #6 $48.59   8.789%   $52.8606   $52.86   $52.85   $52.90  
  Purchase #7 $77.72   11.517%   $86.671   $86.67   $86.65   $86.70  
  7 purchase totals = $882.87       $957.0900   $957.09   $957.05   $957.20