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 $168.81   9.549%   $184.9297   $184.93   $184.95   $184.90  
  Purchase #2 $224.28   6.205%   $238.1966   $238.20   $238.20   $238.20  
  Purchase #3 $136.34   3.771%   $141.4814   $141.48   $141.50   $141.50  
  Purchase #4 $137.98   12.807%   $155.6511   $155.65   $155.65   $155.70  
  Purchase #5 $200.96   3.469%   $207.9313   $207.93   $207.95   $207.90  
  Purchase #6 $55.45   10.522%   $61.2844   $61.28   $61.30   $61.30  
  Purchase #7 $126.95   6.621%   $135.3554   $135.36   $135.35   $135.40  
  7 purchase totals = $1,050.77       $1,124.8299   $1,124.83   $1,124.90   $1,124.90