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 $76.38   8.212%   $82.6523   $82.65   $82.65   $82.70  
  Purchase #2 $157.61   10.631%   $174.3655   $174.37   $174.35   $174.40  
  Purchase #3 $55.27   8.729%   $60.0945   $60.09   $60.10   $60.10  
  Purchase #4 $129.53   6.573%   $138.044   $138.04   $138.05   $138.00  
  Purchase #5 $154.52   13.638%   $175.5934   $175.59   $175.60   $175.60  
  Purchase #6 $160.35   11.262%   $178.4086   $178.41   $178.40   $178.40  
  Purchase #7 $35.46   8.396%   $38.4372   $38.44   $38.45   $38.40  
  7 purchase totals = $769.12       $847.5955   $847.59   $847.60   $847.60