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 $88.98   5.676%   $94.0305   $94.03   $94.05   $94.00  
  Purchase #2 $226.25   10.874%   $250.8524   $250.85   $250.85   $250.90  
  Purchase #3 $167.41   10.711%   $185.3413   $185.34   $185.35   $185.30  
  Purchase #4 $236.58   6.740%   $252.5255   $252.53   $252.55   $252.50  
  Purchase #5 $55.73   11.384%   $62.0743   $62.07   $62.05   $62.10  
  Purchase #6 $248.67   7.522%   $267.375   $267.38   $267.40   $267.40  
  Purchase #7 $169.38   4.764%   $177.4493   $177.45   $177.45   $177.40  
  7 purchase totals = $1,193.00       $1,289.6483   $1,289.65   $1,289.70   $1,289.60