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 $67.53   3.304%   $69.7612   $69.76   $69.75   $69.80  
  Purchase #2 $181.93   6.615%   $193.9647   $193.96   $193.95   $194.00  
  Purchase #3 $95.40   13.488%   $108.2676   $108.27   $108.25   $108.30  
  Purchase #4 $161.76   9.748%   $177.5284   $177.53   $177.55   $177.50  
  Purchase #5 $171.64   4.127%   $178.7236   $178.72   $178.70   $178.70  
  Purchase #6 $230.74   4.399%   $240.8903   $240.89   $240.90   $240.90  
  Purchase #7 $19.53   13.699%   $22.2054   $22.21   $22.20   $22.20  
  7 purchase totals = $928.53       $991.3412   $991.34   $991.30   $991.40