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 $135.76   8.723%   $147.6023   $147.60   $147.60   $147.60  
  Purchase #2 $243.92   6.447%   $259.6455   $259.65   $259.65   $259.60  
  Purchase #3 $116.26   7.547%   $125.0341   $125.03   $125.05   $125.00  
  Purchase #4 $30.78   10.422%   $33.9879   $33.99   $34.00   $34.00  
  Purchase #5 $147.27   4.648%   $154.1151   $154.12   $154.10   $154.10  
  Purchase #6 $183.38   7.290%   $196.7484   $196.75   $196.75   $196.70  
  Purchase #7 $193.77   8.775%   $210.7733   $210.77   $210.75   $210.80  
  7 purchase totals = $1,051.14       $1,127.9066   $1,127.91   $1,127.90   $1,127.80