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 $221.59   11.223%   $246.459   $246.46   $246.45   $246.50  
  Purchase #2 $192.70   7.829%   $207.7865   $207.79   $207.80   $207.80  
  Purchase #3 $54.89   7.417%   $58.9612   $58.96   $58.95   $59.00  
  Purchase #4 $147.80   10.784%   $163.7388   $163.74   $163.75   $163.70  
  Purchase #5 $147.25   6.105%   $156.2396   $156.24   $156.25   $156.20  
  Purchase #6 $12.65   5.550%   $13.3521   $13.35   $13.35   $13.40  
  Purchase #7 $237.45   12.415%   $266.9294   $266.93   $266.95   $266.90  
  7 purchase totals = $1,014.33       $1,113.4666   $1,113.47   $1,113.50   $1,113.50