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 $57.41   13.831%   $65.3504   $65.35   $65.35   $65.40  
  Purchase #2 $217.30   8.400%   $235.5532   $235.55   $235.55   $235.60  
  Purchase #3 $46.75   11.331%   $52.0472   $52.05   $52.05   $52.00  
  Purchase #4 $170.81   8.613%   $185.5219   $185.52   $185.50   $185.50  
  Purchase #5 $22.64   7.391%   $24.3133   $24.31   $24.30   $24.30  
  Purchase #6 $158.70   12.848%   $179.0898   $179.09   $179.10   $179.10  
  Purchase #7 $52.70   7.663%   $56.7384   $56.74   $56.75   $56.70  
  7 purchase totals = $726.31       $798.6142   $798.61   $798.60   $798.60