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 $156.41   7.103%   $167.5198   $167.52   $167.50   $167.50  
  Purchase #2 $23.70   3.595%   $24.552   $24.55   $24.55   $24.60  
  Purchase #3 $187.83   10.536%   $207.6198   $207.62   $207.60   $207.60  
  Purchase #4 $130.77   11.255%   $145.4882   $145.49   $145.50   $145.50  
  Purchase #5 $69.73   13.771%   $79.3325   $79.33   $79.35   $79.30  
  Purchase #6 $191.31   9.217%   $208.943   $208.94   $208.95   $208.90  
  Purchase #7 $137.60   7.790%   $148.319   $148.32   $148.30   $148.30  
  7 purchase totals = $897.35       $981.7743   $981.77   $981.75   $981.70