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 $162.82   11.364%   $181.3229   $181.32   $181.30   $181.30  
  Purchase #2 $248.79   10.296%   $274.4054   $274.41   $274.40   $274.40  
  Purchase #3 $12.73   6.170%   $13.5154   $13.52   $13.50   $13.50  
  Purchase #4 $69.86   13.757%   $79.4706   $79.47   $79.45   $79.50  
  Purchase #5 $73.81   10.663%   $81.6804   $81.68   $81.70   $81.70  
  Purchase #6 $214.62   4.241%   $223.722   $223.72   $223.70   $223.70  
  Purchase #7 $57.28   5.802%   $60.6034   $60.60   $60.60   $60.60  
  7 purchase totals = $839.91       $914.7201   $914.72   $914.65   $914.70