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 $213.90   12.841%   $241.3669   $241.37   $241.35   $241.40  
  Purchase #2 $40.65   8.240%   $43.9996   $44.00   $44.00   $44.00  
  Purchase #3 $120.70   5.252%   $127.0392   $127.04   $127.05   $127.00  
  Purchase #4 $53.89   5.114%   $56.6459   $56.65   $56.65   $56.60  
  Purchase #5 $122.48   10.607%   $135.4715   $135.47   $135.45   $135.50  
  Purchase #6 $198.57   6.633%   $211.7411   $211.74   $211.75   $211.70  
  Purchase #7 $45.55   7.348%   $48.897   $48.90   $48.90   $48.90  
  7 purchase totals = $795.74       $865.1612   $865.17   $865.15   $865.10