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 $158.72   11.683%   $177.2633   $177.26   $177.25   $177.30  
  Purchase #2 $53.53   5.654%   $56.5566   $56.56   $56.55   $56.60  
  Purchase #3 $92.59   3.430%   $95.7658   $95.77   $95.75   $95.80  
  Purchase #4 $176.83   5.458%   $186.4814   $186.48   $186.50   $186.50  
  Purchase #5 $155.93   4.379%   $162.7582   $162.76   $162.75   $162.80  
  Purchase #6 $213.93   10.664%   $236.7435   $236.74   $236.75   $236.70  
  Purchase #7 $31.35   12.319%   $35.212   $35.21   $35.20   $35.20  
  7 purchase totals = $882.88       $950.7808   $950.78   $950.75   $950.90