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 $147.77   10.684%   $163.5577   $163.56   $163.55   $163.60  
  Purchase #2 $184.75   4.727%   $193.4831   $193.48   $193.50   $193.50  
  Purchase #3 $238.33   5.423%   $251.2546   $251.25   $251.25   $251.30  
  Purchase #4 $208.49   6.645%   $222.3442   $222.34   $222.35   $222.30  
  Purchase #5 $68.79   11.863%   $76.9506   $76.95   $76.95   $77.00  
  Purchase #6 $219.59   13.635%   $249.5311   $249.53   $249.55   $249.50  
  Purchase #7 $59.47   13.217%   $67.3301   $67.33   $67.35   $67.30  
  7 purchase totals = $1,127.19       $1,224.4514   $1,224.44   $1,224.50   $1,224.50