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 $157.34   5.531%   $166.0425   $166.04   $166.05   $166.00  
  Purchase #2 $236.89   13.729%   $269.4126   $269.41   $269.40   $269.40  
  Purchase #3 $41.30   8.744%   $44.9113   $44.91   $44.90   $44.90  
  Purchase #4 $176.97   11.251%   $196.8809   $196.88   $196.90   $196.90  
  Purchase #5 $237.88   13.161%   $269.1874   $269.19   $269.20   $269.20  
  Purchase #6 $124.55   10.516%   $137.6477   $137.65   $137.65   $137.60  
  Purchase #7 $169.72   8.580%   $184.282   $184.28   $184.30   $184.30  
  7 purchase totals = $1,144.65       $1,268.3644   $1,268.36   $1,268.40   $1,268.30