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 $112.67   6.110%   $119.5541   $119.55   $119.55   $119.60  
  Purchase #2 $70.94   5.382%   $74.758   $74.76   $74.75   $74.80  
  Purchase #3 $83.62   3.791%   $86.79   $86.79   $86.80   $86.80  
  Purchase #4 $159.52   6.501%   $169.8904   $169.89   $169.90   $169.90  
  Purchase #5 $122.36   6.332%   $130.1078   $130.11   $130.10   $130.10  
  Purchase #6 $238.30   11.730%   $266.2526   $266.25   $266.25   $266.30  
  Purchase #7 $112.45   12.668%   $126.6952   $126.70   $126.70   $126.70  
  7 purchase totals = $899.86       $974.0481   $974.05   $974.05   $974.20