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 $54.35   13.726%   $61.8101   $61.81   $61.80   $61.80  
  Purchase #2 $49.29   13.453%   $55.921   $55.92   $55.90   $55.90  
  Purchase #3 $227.65   4.534%   $237.9717   $237.97   $237.95   $238.00  
  Purchase #4 $65.26   3.552%   $67.578   $67.58   $67.60   $67.60  
  Purchase #5 $80.84   3.569%   $83.7252   $83.73   $83.75   $83.70  
  Purchase #6 $129.44   9.310%   $141.4909   $141.49   $141.50   $141.50  
  Purchase #7 $235.83   5.162%   $248.0035   $248.00   $248.00   $248.00  
  7 purchase totals = $842.66       $896.5004   $896.50   $896.50   $896.50