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 $53.52   13.605%   $60.8014   $60.80   $60.80   $60.80  
  Purchase #2 $174.44   11.212%   $193.9982   $194.00   $194.00   $194.00  
  Purchase #3 $115.37   3.793%   $119.746   $119.75   $119.75   $119.70  
  Purchase #4 $176.74   7.714%   $190.3737   $190.37   $190.35   $190.40  
  Purchase #5 $49.32   8.676%   $53.599   $53.60   $53.60   $53.60  
  Purchase #6 $173.41   3.150%   $178.8724   $178.87   $178.85   $178.90  
  Purchase #7 $41.86   9.632%   $45.892   $45.89   $45.90   $45.90  
  7 purchase totals = $784.66       $843.2827   $843.28   $843.25   $843.30