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 $212.66   6.162%   $225.7641   $225.76   $225.75   $225.80  
  Purchase #2 $191.56   6.307%   $203.6417   $203.64   $203.65   $203.60  
  Purchase #3 $132.86   7.859%   $143.3015   $143.30   $143.30   $143.30  
  Purchase #4 $154.58   9.186%   $168.7797   $168.78   $168.80   $168.80  
  Purchase #5 $110.80   5.422%   $116.8076   $116.81   $116.80   $116.80  
  Purchase #6 $13.76   11.555%   $15.35   $15.35   $15.35   $15.40  
  Purchase #7 $24.32   5.349%   $25.6209   $25.62   $25.60   $25.60  
  7 purchase totals = $840.54       $899.2655   $899.26   $899.25   $899.30