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 $134.37   13.605%   $152.651   $152.65   $152.65   $152.70  
  Purchase #2 $250.45   6.442%   $266.584   $266.58   $266.60   $266.60  
  Purchase #3 $245.29   5.501%   $258.7834   $258.78   $258.80   $258.80  
  Purchase #4 $57.81   13.507%   $65.6184   $65.62   $65.60   $65.60  
  Purchase #5 $150.66   11.332%   $167.7328   $167.73   $167.75   $167.70  
  Purchase #6 $185.43   13.540%   $210.5372   $210.54   $210.55   $210.50  
  Purchase #7 $30.38   8.577%   $32.9857   $32.99   $33.00   $33.00  
  7 purchase totals = $1,054.39       $1,154.8925   $1,154.89   $1,154.95   $1,154.90