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 $169.89   12.738%   $191.5306   $191.53   $191.55   $191.50  
  Purchase #2 $149.99   4.307%   $156.4501   $156.45   $156.45   $156.50  
  Purchase #3 $33.44   3.487%   $34.6061   $34.61   $34.60   $34.60  
  Purchase #4 $76.70   4.785%   $80.3701   $80.37   $80.35   $80.40  
  Purchase #5 $141.83   8.201%   $153.4615   $153.46   $153.45   $153.50  
  Purchase #6 $246.56   9.447%   $269.8525   $269.85   $269.85   $269.90  
  Purchase #7 $154.28   4.610%   $161.3923   $161.39   $161.40   $161.40  
  7 purchase totals = $972.69       $1,047.6632   $1,047.66   $1,047.65   $1,047.80