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 $85.86   9.281%   $93.8287   $93.83   $93.85   $93.80  
  Purchase #2 $149.97   10.255%   $165.3494   $165.35   $165.35   $165.30  
  Purchase #3 $163.90   4.119%   $170.651   $170.65   $170.65   $170.70  
  Purchase #4 $239.79   3.500%   $248.1827   $248.18   $248.20   $248.20  
  Purchase #5 $101.91   12.626%   $114.7772   $114.78   $114.80   $114.80  
  Purchase #6 $19.30   6.643%   $20.5821   $20.58   $20.60   $20.60  
  Purchase #7 $221.74   3.338%   $229.1417   $229.14   $229.15   $229.10  
  7 purchase totals = $982.47       $1,042.5128   $1,042.51   $1,042.60   $1,042.50