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 $84.45   11.699%   $94.3298   $94.33   $94.35   $94.30  
  Purchase #2 $127.70   4.211%   $133.0774   $133.08   $133.10   $133.10  
  Purchase #3 $176.89   4.393%   $184.6608   $184.66   $184.65   $184.70  
  Purchase #4 $244.64   3.247%   $252.5835   $252.58   $252.60   $252.60  
  Purchase #5 $153.64   11.471%   $171.264   $171.26   $171.25   $171.30  
  Purchase #6 $116.73   13.725%   $132.7512   $132.75   $132.75   $132.80  
  Purchase #7 $50.35   7.535%   $54.1439   $54.14   $54.15   $54.10  
  7 purchase totals = $954.40       $1,022.8106   $1,022.80   $1,022.85   $1,022.90