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 $205.61   10.164%   $226.5082   $226.51   $226.50   $226.50  
  Purchase #2 $62.48   5.307%   $65.7958   $65.80   $65.80   $65.80  
  Purchase #3 $240.61   10.490%   $265.85   $265.85   $265.85   $265.90  
  Purchase #4 $63.38   3.825%   $65.8043   $65.80   $65.80   $65.80  
  Purchase #5 $45.85   10.344%   $50.5927   $50.59   $50.60   $50.60  
  Purchase #6 $215.71   7.746%   $232.4189   $232.42   $232.40   $232.40  
  Purchase #7 $115.99   10.102%   $127.7073   $127.71   $127.70   $127.70  
  7 purchase totals = $949.63       $1,034.6772   $1,034.68   $1,034.65   $1,034.70