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 $109.94   12.377%   $123.5473   $123.55   $123.55   $123.50  
  Purchase #2 $180.53   9.465%   $197.6172   $197.62   $197.60   $197.60  
  Purchase #3 $220.30   12.712%   $248.3045   $248.30   $248.30   $248.30  
  Purchase #4 $131.93   8.650%   $143.3419   $143.34   $143.35   $143.30  
  Purchase #5 $155.66   11.694%   $173.8629   $173.86   $173.85   $173.90  
  Purchase #6 $93.94   6.621%   $100.1598   $100.16   $100.15   $100.20  
  Purchase #7 $45.29   8.841%   $49.2941   $49.29   $49.30   $49.30  
  7 purchase totals = $937.59       $1,036.1277   $1,036.12   $1,036.10   $1,036.10