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 $80.75   6.437%   $85.9479   $85.95   $85.95   $85.90  
  Purchase #2 $53.54   10.114%   $58.955   $58.96   $58.95   $59.00  
  Purchase #3 $116.86   11.191%   $129.9378   $129.94   $129.95   $129.90  
  Purchase #4 $120.46   10.277%   $132.8397   $132.84   $132.85   $132.80  
  Purchase #5 $149.78   9.387%   $163.8398   $163.84   $163.85   $163.80  
  Purchase #6 $218.92   13.458%   $248.3823   $248.38   $248.40   $248.40  
  Purchase #7 $231.50   6.848%   $247.3531   $247.35   $247.35   $247.40  
  7 purchase totals = $971.81       $1,067.2556   $1,067.26   $1,067.30   $1,067.20