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 $84.73   10.124%   $93.3081   $93.31   $93.30   $93.30  
  Purchase #2 $185.42   8.633%   $201.4273   $201.43   $201.45   $201.40  
  Purchase #3 $33.50   11.141%   $37.2322   $37.23   $37.25   $37.20  
  Purchase #4 $22.83   4.806%   $23.9272   $23.93   $23.95   $23.90  
  Purchase #5 $217.99   3.586%   $225.8071   $225.81   $225.80   $225.80  
  Purchase #6 $121.29   10.639%   $134.194   $134.19   $134.20   $134.20  
  Purchase #7 $190.48   5.181%   $200.3488   $200.35   $200.35   $200.30  
  7 purchase totals = $856.24       $916.2447   $916.25   $916.30   $916.10