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 $171.71   13.870%   $195.5262   $195.53   $195.55   $195.50  
  Purchase #2 $245.25   8.789%   $266.805   $266.81   $266.80   $266.80  
  Purchase #3 $108.52   6.337%   $115.3969   $115.40   $115.40   $115.40  
  Purchase #4 $117.87   10.228%   $129.9257   $129.93   $129.95   $129.90  
  Purchase #5 $81.90   10.864%   $90.7976   $90.80   $90.80   $90.80  
  Purchase #6 $155.49   12.186%   $174.438   $174.44   $174.45   $174.40  
  Purchase #7 $194.37   13.130%   $219.8908   $219.89   $219.90   $219.90  
  7 purchase totals = $1,075.11       $1,192.7802   $1,192.80   $1,192.85   $1,192.70