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 $91.67   5.286%   $96.5157   $96.52   $96.50   $96.50  
  Purchase #2 $54.84   8.261%   $59.3703   $59.37   $59.35   $59.40  
  Purchase #3 $170.97   6.600%   $182.254   $182.25   $182.25   $182.30  
  Purchase #4 $167.89   4.807%   $175.9605   $175.96   $175.95   $176.00  
  Purchase #5 $39.66   7.487%   $42.6293   $42.63   $42.65   $42.60  
  Purchase #6 $200.64   10.403%   $221.5126   $221.51   $221.50   $221.50  
  Purchase #7 $76.95   6.314%   $81.8086   $81.81   $81.80   $81.80  
  7 purchase totals = $802.62       $860.0510   $860.05   $860.00   $860.10