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 $44.52   13.626%   $50.5863   $50.59   $50.60   $50.60  
  Purchase #2 $185.52   11.526%   $206.903   $206.90   $206.90   $206.90  
  Purchase #3 $115.98   10.463%   $128.115   $128.12   $128.10   $128.10  
  Purchase #4 $53.87   12.679%   $60.7002   $60.70   $60.70   $60.70  
  Purchase #5 $177.68   3.769%   $184.3768   $184.38   $184.40   $184.40  
  Purchase #6 $156.83   5.233%   $165.0369   $165.04   $165.05   $165.00  
  Purchase #7 $26.80   5.560%   $28.2901   $28.29   $28.30   $28.30  
  7 purchase totals = $761.20       $824.0083   $824.02   $824.05   $824.00