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 $61.33   13.451%   $69.5795   $69.58   $69.60   $69.60  
  Purchase #2 $114.69   3.266%   $118.4358   $118.44   $118.45   $118.40  
  Purchase #3 $169.32   9.315%   $185.0922   $185.09   $185.10   $185.10  
  Purchase #4 $56.47   13.403%   $64.0387   $64.04   $64.05   $64.00  
  Purchase #5 $86.28   6.445%   $91.8407   $91.84   $91.85   $91.80  
  Purchase #6 $25.33   11.141%   $28.152   $28.15   $28.15   $28.20  
  Purchase #7 $14.42   11.246%   $16.0417   $16.04   $16.05   $16.00  
  7 purchase totals = $527.84       $573.1806   $573.18   $573.25   $573.10