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 $171.95   8.534%   $186.6242   $186.62   $186.60   $186.60  
  Purchase #2 $39.59   10.385%   $43.7014   $43.70   $43.70   $43.70  
  Purchase #3 $73.41   12.168%   $82.3425   $82.34   $82.35   $82.30  
  Purchase #4 $114.56   8.299%   $124.0673   $124.07   $124.05   $124.10  
  Purchase #5 $140.58   11.196%   $156.3193   $156.32   $156.30   $156.30  
  Purchase #6 $92.58   6.353%   $98.4616   $98.46   $98.45   $98.50  
  Purchase #7 $62.54   8.170%   $67.6495   $67.65   $67.65   $67.60  
  7 purchase totals = $695.21       $759.1658   $759.16   $759.10   $759.10