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 $119.35   6.373%   $126.9562   $126.96   $126.95   $127.00  
  Purchase #2 $230.44   13.633%   $261.8559   $261.86   $261.85   $261.90  
  Purchase #3 $180.85   13.270%   $204.8488   $204.85   $204.85   $204.80  
  Purchase #4 $139.65   11.589%   $155.834   $155.83   $155.85   $155.80  
  Purchase #5 $78.87   13.320%   $89.3755   $89.38   $89.40   $89.40  
  Purchase #6 $200.94   7.534%   $216.0788   $216.08   $216.10   $216.10  
  Purchase #7 $241.49   13.553%   $274.2191   $274.22   $274.20   $274.20  
  7 purchase totals = $1,191.59       $1,329.1683   $1,329.18   $1,329.20   $1,329.20