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 $50.58   13.356%   $57.3355   $57.34   $57.35   $57.30  
  Purchase #2 $226.76   11.873%   $253.6832   $253.68   $253.70   $253.70  
  Purchase #3 $134.42   7.199%   $144.0969   $144.10   $144.10   $144.10  
  Purchase #4 $47.39   13.448%   $53.763   $53.76   $53.75   $53.80  
  Purchase #5 $149.43   12.687%   $168.3882   $168.39   $168.40   $168.40  
  Purchase #6 $192.73   11.717%   $215.3122   $215.31   $215.30   $215.30  
  Purchase #7 $152.77   12.453%   $171.7944   $171.79   $171.80   $171.80  
  7 purchase totals = $954.08       $1,064.3734   $1,064.37   $1,064.40   $1,064.40