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 $180.33   13.662%   $204.9667   $204.97   $204.95   $205.00  
  Purchase #2 $150.45   9.303%   $164.4464   $164.45   $164.45   $164.40  
  Purchase #3 $129.86   8.809%   $141.2994   $141.30   $141.30   $141.30  
  Purchase #4 $181.34   6.710%   $193.5079   $193.51   $193.50   $193.50  
  Purchase #5 $145.67   13.107%   $164.763   $164.76   $164.75   $164.80  
  Purchase #6 $173.79   13.312%   $196.9249   $196.92   $196.90   $196.90  
  Purchase #7 $7.72   8.413%   $8.3695   $8.37   $8.35   $8.40  
  7 purchase totals = $969.16       $1,074.2778   $1,074.28   $1,074.20   $1,074.30