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 $63.49   9.642%   $69.6117   $69.61   $69.60   $69.60  
  Purchase #2 $246.93   7.698%   $265.9387   $265.94   $265.95   $265.90  
  Purchase #3 $87.93   7.607%   $94.6188   $94.62   $94.60   $94.60  
  Purchase #4 $48.97   9.281%   $53.5149   $53.51   $53.50   $53.50  
  Purchase #5 $32.76   10.493%   $36.1975   $36.20   $36.20   $36.20  
  Purchase #6 $190.95   7.595%   $205.4527   $205.45   $205.45   $205.50  
  Purchase #7 $162.79   11.227%   $181.0664   $181.07   $181.05   $181.10  
  7 purchase totals = $833.82       $906.4007   $906.40   $906.35   $906.40