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 $238.54   12.191%   $267.6204   $267.62   $267.60   $267.60  
  Purchase #2 $65.35   9.661%   $71.6635   $71.66   $71.65   $71.70  
  Purchase #3 $89.29   9.692%   $97.944   $97.94   $97.95   $97.90  
  Purchase #4 $137.29   4.438%   $143.3829   $143.38   $143.40   $143.40  
  Purchase #5 $186.40   7.311%   $200.0277   $200.03   $200.05   $200.00  
  Purchase #6 $80.42   8.589%   $87.3273   $87.33   $87.35   $87.30  
  Purchase #7 $165.30   11.149%   $183.7293   $183.73   $183.75   $183.70  
  7 purchase totals = $962.59       $1,051.6951   $1,051.69   $1,051.75   $1,051.60