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 $65.39   12.453%   $73.533   $73.53   $73.55   $73.50  
  Purchase #2 $41.63   8.456%   $45.1502   $45.15   $45.15   $45.20  
  Purchase #3 $56.41   10.706%   $62.4493   $62.45   $62.45   $62.40  
  Purchase #4 $133.84   13.845%   $152.3701   $152.37   $152.35   $152.40  
  Purchase #5 $248.76   6.377%   $264.6234   $264.62   $264.60   $264.60  
  Purchase #6 $233.68   6.419%   $248.6799   $248.68   $248.70   $248.70  
  Purchase #7 $155.55   9.505%   $170.335   $170.34   $170.35   $170.30  
  7 purchase totals = $935.26       $1,017.1409   $1,017.14   $1,017.15   $1,017.10