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 $177.66   9.437%   $194.4258   $194.43   $194.45   $194.40  
  Purchase #2 $52.60   7.734%   $56.6681   $56.67   $56.65   $56.70  
  Purchase #3 $227.30   9.508%   $248.9117   $248.91   $248.90   $248.90  
  Purchase #4 $213.96   6.458%   $227.7775   $227.78   $227.80   $227.80  
  Purchase #5 $32.96   8.103%   $35.6307   $35.63   $35.65   $35.60  
  Purchase #6 $31.49   10.280%   $34.7272   $34.73   $34.75   $34.70  
  Purchase #7 $210.78   11.604%   $235.2389   $235.24   $235.25   $235.20  
  7 purchase totals = $946.75       $1,033.3799   $1,033.39   $1,033.45   $1,033.30