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 $219.99   6.162%   $233.5458   $233.55   $233.55   $233.50  
  Purchase #2 $200.56   4.578%   $209.7416   $209.74   $209.75   $209.70  
  Purchase #3 $117.62   3.256%   $121.4497   $121.45   $121.45   $121.40  
  Purchase #4 $44.98   9.521%   $49.2625   $49.26   $49.25   $49.30  
  Purchase #5 $28.98   13.835%   $32.9894   $32.99   $33.00   $33.00  
  Purchase #6 $141.71   9.756%   $155.5352   $155.54   $155.55   $155.50  
  Purchase #7 $228.57   10.406%   $252.355   $252.36   $252.35   $252.40  
  7 purchase totals = $982.41       $1,054.8792   $1,054.89   $1,054.90   $1,054.80