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 $38.51   7.624%   $41.446   $41.45   $41.45   $41.40  
  Purchase #2 $49.93   9.311%   $54.579   $54.58   $54.60   $54.60  
  Purchase #3 $172.33   12.135%   $193.2422   $193.24   $193.25   $193.20  
  Purchase #4 $160.81   3.202%   $165.9591   $165.96   $165.95   $166.00  
  Purchase #5 $110.83   5.226%   $116.622   $116.62   $116.60   $116.60  
  Purchase #6 $157.33   5.486%   $165.9611   $165.96   $165.95   $166.00  
  Purchase #7 $111.37   8.751%   $121.116   $121.12   $121.10   $121.10  
  7 purchase totals = $801.11       $858.9254   $858.93   $858.90   $858.90