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 $190.69   8.528%   $206.952   $206.95   $206.95   $207.00  
  Purchase #2 $22.76   9.598%   $24.9445   $24.94   $24.95   $24.90  
  Purchase #3 $227.80   7.599%   $245.1105   $245.11   $245.10   $245.10  
  Purchase #4 $156.46   9.428%   $171.211   $171.21   $171.20   $171.20  
  Purchase #5 $121.65   4.798%   $127.4868   $127.49   $127.50   $127.50  
  Purchase #6 $74.45   5.330%   $78.4182   $78.42   $78.40   $78.40  
  Purchase #7 $56.47   7.194%   $60.5325   $60.53   $60.55   $60.50  
  7 purchase totals = $850.28       $914.6555   $914.65   $914.65   $914.60