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 $25.96   12.768%   $29.2746   $29.27   $29.25   $29.30  
  Purchase #2 $222.90   8.195%   $241.1667   $241.17   $241.15   $241.20  
  Purchase #3 $33.77   5.135%   $35.5041   $35.50   $35.50   $35.50  
  Purchase #4 $218.79   13.401%   $248.11   $248.11   $248.10   $248.10  
  Purchase #5 $243.30   13.200%   $275.4156   $275.42   $275.40   $275.40  
  Purchase #6 $63.37   3.302%   $65.4625   $65.46   $65.45   $65.50  
  Purchase #7 $113.30   11.435%   $126.2559   $126.26   $126.25   $126.30  
  7 purchase totals = $921.39       $1,021.1894   $1,021.19   $1,021.10   $1,021.30