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 $30.66   6.779%   $32.7384   $32.74   $32.75   $32.70  
  Purchase #2 $151.43   6.530%   $161.3184   $161.32   $161.30   $161.30  
  Purchase #3 $75.93   11.517%   $84.6749   $84.67   $84.65   $84.70  
  Purchase #4 $160.42   13.810%   $182.574   $182.57   $182.55   $182.60  
  Purchase #5 $123.82   13.480%   $140.5109   $140.51   $140.50   $140.50  
  Purchase #6 $241.39   12.546%   $271.6748   $271.67   $271.65   $271.70  
  Purchase #7 $163.82   13.143%   $185.3509   $185.35   $185.35   $185.40  
  7 purchase totals = $947.47       $1,058.8423   $1,058.83   $1,058.75   $1,058.90