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 $208.52   5.658%   $220.3181   $220.32   $220.30   $220.30  
  Purchase #2 $224.46   5.347%   $236.4619   $236.46   $236.45   $236.50  
  Purchase #3 $211.85   5.158%   $222.7772   $222.78   $222.80   $222.80  
  Purchase #4 $192.82   10.581%   $213.2223   $213.22   $213.20   $213.20  
  Purchase #5 $147.50   6.229%   $156.6878   $156.69   $156.70   $156.70  
  Purchase #6 $227.43   6.774%   $242.8361   $242.84   $242.85   $242.80  
  Purchase #7 $214.37   13.382%   $243.057   $243.06   $243.05   $243.10  
  7 purchase totals = $1,426.95       $1,535.3604   $1,535.37   $1,535.35   $1,535.40