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 $59.96   3.188%   $61.8715   $61.87   $61.85   $61.90  
  Purchase #2 $226.52   10.674%   $250.6987   $250.70   $250.70   $250.70  
  Purchase #3 $121.35   12.831%   $136.9204   $136.92   $136.90   $136.90  
  Purchase #4 $142.56   10.755%   $157.8923   $157.89   $157.90   $157.90  
  Purchase #5 $77.45   3.432%   $80.1081   $80.11   $80.10   $80.10  
  Purchase #6 $104.85   13.837%   $119.3581   $119.36   $119.35   $119.40  
  Purchase #7 $195.48   9.737%   $214.5139   $214.51   $214.50   $214.50  
  7 purchase totals = $928.17       $1,021.3630   $1,021.36   $1,021.30   $1,021.40