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 $152.36   7.218%   $163.3573   $163.36   $163.35   $163.40  
  Purchase #2 $85.66   13.681%   $97.3791   $97.38   $97.40   $97.40  
  Purchase #3 $176.75   5.573%   $186.6003   $186.60   $186.60   $186.60  
  Purchase #4 $161.56   6.324%   $171.7771   $171.78   $171.80   $171.80  
  Purchase #5 $110.99   3.541%   $114.9202   $114.92   $114.90   $114.90  
  Purchase #6 $192.91   3.171%   $199.0272   $199.03   $199.05   $199.00  
  Purchase #7 $82.27   13.731%   $93.5665   $93.57   $93.55   $93.60  
  7 purchase totals = $962.50       $1,026.6277   $1,026.64   $1,026.65   $1,026.70