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 $52.71   10.528%   $58.2593   $58.26   $58.25   $58.30  
  Purchase #2 $72.53   5.272%   $76.3538   $76.35   $76.35   $76.40  
  Purchase #3 $108.30   9.682%   $118.7856   $118.79   $118.80   $118.80  
  Purchase #4 $166.29   6.668%   $177.3782   $177.38   $177.40   $177.40  
  Purchase #5 $83.48   4.572%   $87.2967   $87.30   $87.30   $87.30  
  Purchase #6 $242.87   10.722%   $268.9105   $268.91   $268.90   $268.90  
  Purchase #7 $231.84   7.258%   $248.6669   $248.67   $248.65   $248.70  
  7 purchase totals = $958.02       $1,035.6510   $1,035.66   $1,035.65   $1,035.80