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 $87.54   10.688%   $96.8963   $96.90   $96.90   $96.90  
  Purchase #2 $128.52   5.728%   $135.8816   $135.88   $135.90   $135.90  
  Purchase #3 $41.41   3.527%   $42.8705   $42.87   $42.85   $42.90  
  Purchase #4 $244.46   8.727%   $265.794   $265.79   $265.80   $265.80  
  Purchase #5 $50.39   12.835%   $56.8576   $56.86   $56.85   $56.90  
  Purchase #6 $163.25   6.477%   $173.8237   $173.82   $173.80   $173.80  
  Purchase #7 $222.46   6.869%   $237.7408   $237.74   $237.75   $237.70  
  7 purchase totals = $938.03       $1,009.8645   $1,009.86   $1,009.85   $1,009.90