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 $163.47   3.763%   $169.6214   $169.62   $169.60   $169.60  
  Purchase #2 $180.40   12.644%   $203.2098   $203.21   $203.20   $203.20  
  Purchase #3 $68.32   8.497%   $74.1252   $74.13   $74.15   $74.10  
  Purchase #4 $110.58   5.434%   $116.5889   $116.59   $116.60   $116.60  
  Purchase #5 $107.58   6.177%   $114.2252   $114.23   $114.25   $114.20  
  Purchase #6 $134.48   12.134%   $150.7978   $150.80   $150.80   $150.80  
  Purchase #7 $183.93   12.555%   $207.0224   $207.02   $207.00   $207.00  
  7 purchase totals = $948.76       $1,035.5907   $1,035.60   $1,035.60   $1,035.50