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 $241.33   6.194%   $256.278   $256.28   $256.30   $256.30  
  Purchase #2 $230.75   12.145%   $258.7746   $258.77   $258.75   $258.80  
  Purchase #3 $7.25   13.655%   $8.24   $8.24   $8.25   $8.20  
  Purchase #4 $214.77   6.535%   $228.8052   $228.81   $228.80   $228.80  
  Purchase #5 $164.56   6.529%   $175.3041   $175.30   $175.30   $175.30  
  Purchase #6 $96.68   13.697%   $109.9223   $109.92   $109.90   $109.90  
  Purchase #7 $68.92   9.754%   $75.6425   $75.64   $75.65   $75.60  
  7 purchase totals = $1,024.26       $1,112.9667   $1,112.96   $1,112.95   $1,112.90