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 $56.55   9.538%   $61.9437   $61.94   $61.95   $61.90  
  Purchase #2 $77.68   4.517%   $81.1888   $81.19   $81.20   $81.20  
  Purchase #3 $204.25   6.239%   $216.9932   $216.99   $217.00   $217.00  
  Purchase #4 $151.25   4.442%   $157.9685   $157.97   $157.95   $158.00  
  Purchase #5 $122.40   11.102%   $135.9888   $135.99   $136.00   $136.00  
  Purchase #6 $203.35   12.602%   $228.9762   $228.98   $229.00   $229.00  
  Purchase #7 $134.48   4.492%   $140.5208   $140.52   $140.50   $140.50  
  7 purchase totals = $949.96       $1,023.5800   $1,023.58   $1,023.60   $1,023.60