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 $187.86   11.834%   $210.0914   $210.09   $210.10   $210.10  
  Purchase #2 $249.95   9.774%   $274.3801   $274.38   $274.40   $274.40  
  Purchase #3 $38.31   6.405%   $40.7638   $40.76   $40.75   $40.80  
  Purchase #4 $27.74   7.137%   $29.7198   $29.72   $29.70   $29.70  
  Purchase #5 $67.71   9.710%   $74.2846   $74.28   $74.30   $74.30  
  Purchase #6 $60.39   8.652%   $65.6149   $65.61   $65.60   $65.60  
  Purchase #7 $241.56   5.771%   $255.5004   $255.50   $255.50   $255.50  
  7 purchase totals = $873.52       $950.3550   $950.34   $950.35   $950.40