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 $33.39   10.759%   $36.9824   $36.98   $37.00   $37.00  
  Purchase #2 $142.83   8.112%   $154.4164   $154.42   $154.40   $154.40  
  Purchase #3 $69.62   8.458%   $75.5085   $75.51   $75.50   $75.50  
  Purchase #4 $208.29   12.570%   $234.4721   $234.47   $234.45   $234.50  
  Purchase #5 $196.26   3.262%   $202.662   $202.66   $202.65   $202.70  
  Purchase #6 $241.59   9.439%   $264.3937   $264.39   $264.40   $264.40  
  Purchase #7 $42.95   9.173%   $46.8898   $46.89   $46.90   $46.90  
  7 purchase totals = $934.93       $1,015.3249   $1,015.32   $1,015.30   $1,015.40