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 $237.37   4.701%   $248.5288   $248.53   $248.55   $248.50  
  Purchase #2 $53.76   4.727%   $56.3012   $56.30   $56.30   $56.30  
  Purchase #3 $234.93   8.435%   $254.7463   $254.75   $254.75   $254.70  
  Purchase #4 $60.44   10.520%   $66.7983   $66.80   $66.80   $66.80  
  Purchase #5 $144.41   7.269%   $154.9072   $154.91   $154.90   $154.90  
  Purchase #6 $158.45   10.224%   $174.6499   $174.65   $174.65   $174.60  
  Purchase #7 $74.50   5.479%   $78.5819   $78.58   $78.60   $78.60  
  7 purchase totals = $963.86       $1,034.5136   $1,034.52   $1,034.55   $1,034.40