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 $26.36   11.640%   $29.4283   $29.43   $29.45   $29.40  
  Purchase #2 $155.61   6.455%   $165.6546   $165.65   $165.65   $165.70  
  Purchase #3 $214.25   5.679%   $226.4173   $226.42   $226.40   $226.40  
  Purchase #4 $166.61   12.671%   $187.7212   $187.72   $187.70   $187.70  
  Purchase #5 $118.98   4.373%   $124.183   $124.18   $124.20   $124.20  
  Purchase #6 $148.83   3.132%   $153.4914   $153.49   $153.50   $153.50  
  Purchase #7 $142.90   13.605%   $162.3415   $162.34   $162.35   $162.30  
  7 purchase totals = $973.54       $1,049.2373   $1,049.23   $1,049.25   $1,049.20