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 $95.89   12.202%   $107.5905   $107.59   $107.60   $107.60  
  Purchase #2 $235.84   6.212%   $250.4904   $250.49   $250.50   $250.50  
  Purchase #3 $84.70   12.246%   $95.0724   $95.07   $95.05   $95.10  
  Purchase #4 $178.31   8.439%   $193.3576   $193.36   $193.35   $193.40  
  Purchase #5 $56.87   4.819%   $59.6106   $59.61   $59.60   $59.60  
  Purchase #6 $202.55   9.586%   $221.9664   $221.97   $221.95   $222.00  
  Purchase #7 $42.80   9.809%   $46.9983   $47.00   $47.00   $47.00  
  7 purchase totals = $896.96       $975.0862   $975.09   $975.05   $975.20