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 $216.47   12.694%   $243.9487   $243.95   $243.95   $243.90  
  Purchase #2 $88.54   9.339%   $96.8088   $96.81   $96.80   $96.80  
  Purchase #3 $236.46   6.359%   $251.4965   $251.50   $251.50   $251.50  
  Purchase #4 $124.68   7.837%   $134.4512   $134.45   $134.45   $134.50  
  Purchase #5 $108.91   13.723%   $123.8557   $123.86   $123.85   $123.90  
  Purchase #6 $180.28   8.626%   $195.831   $195.83   $195.85   $195.80  
  Purchase #7 $35.35   12.307%   $39.7005   $39.70   $39.70   $39.70  
  7 purchase totals = $990.69       $1,086.0924   $1,086.10   $1,086.10   $1,086.10