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 $63.64   12.148%   $71.371   $71.37   $71.35   $71.40  
  Purchase #2 $123.48   7.655%   $132.9324   $132.93   $132.95   $132.90  
  Purchase #3 $90.37   4.192%   $94.1583   $94.16   $94.15   $94.20  
  Purchase #4 $240.33   3.302%   $248.2657   $248.27   $248.25   $248.30  
  Purchase #5 $193.28   7.448%   $207.6755   $207.68   $207.70   $207.70  
  Purchase #6 $33.72   4.631%   $35.2816   $35.28   $35.30   $35.30  
  Purchase #7 $154.45   10.643%   $170.8881   $170.89   $170.90   $170.90  
  7 purchase totals = $899.27       $960.5726   $960.58   $960.60   $960.70