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 $91.38   4.311%   $95.3194   $95.32   $95.30   $95.30  
  Purchase #2 $16.84   11.103%   $18.7097   $18.71   $18.70   $18.70  
  Purchase #3 $236.32   10.643%   $261.4715   $261.47   $261.45   $261.50  
  Purchase #4 $160.79   4.207%   $167.5544   $167.55   $167.55   $167.60  
  Purchase #5 $133.40   10.433%   $147.3176   $147.32   $147.30   $147.30  
  Purchase #6 $239.74   8.113%   $259.1901   $259.19   $259.20   $259.20  
  Purchase #7 $38.52   5.579%   $40.669   $40.67   $40.65   $40.70  
  7 purchase totals = $916.99       $990.2317   $990.23   $990.15   $990.30