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 $201.89   6.119%   $214.2436   $214.24   $214.25   $214.20  
  Purchase #2 $27.43   11.655%   $30.627   $30.63   $30.65   $30.60  
  Purchase #3 $178.99   13.319%   $202.8297   $202.83   $202.85   $202.80  
  Purchase #4 $153.69   13.298%   $174.1277   $174.13   $174.15   $174.10  
  Purchase #5 $190.44   6.553%   $202.9195   $202.92   $202.90   $202.90  
  Purchase #6 $182.64   12.324%   $205.1486   $205.15   $205.15   $205.10  
  Purchase #7 $39.58   10.138%   $43.5926   $43.59   $43.60   $43.60  
  7 purchase totals = $974.66       $1,073.4887   $1,073.49   $1,073.55   $1,073.30