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 $180.74   6.332%   $192.1845   $192.18   $192.20   $192.20  
  Purchase #2 $212.77   11.705%   $237.6747   $237.67   $237.65   $237.70  
  Purchase #3 $135.51   12.773%   $152.8187   $152.82   $152.80   $152.80  
  Purchase #4 $44.82   3.321%   $46.3085   $46.31   $46.30   $46.30  
  Purchase #5 $169.75   4.599%   $177.5568   $177.56   $177.55   $177.60  
  Purchase #6 $106.51   4.806%   $111.6289   $111.63   $111.65   $111.60  
  Purchase #7 $88.57   4.469%   $92.5282   $92.53   $92.55   $92.50  
  7 purchase totals = $938.67       $1,010.7003   $1,010.70   $1,010.70   $1,010.70