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 $73.96   12.623%   $83.296   $83.30   $83.30   $83.30  
  Purchase #2 $222.68   10.326%   $245.6739   $245.67   $245.65   $245.70  
  Purchase #3 $116.59   13.779%   $132.6549   $132.65   $132.65   $132.70  
  Purchase #4 $208.34   8.106%   $225.228   $225.23   $225.25   $225.20  
  Purchase #5 $196.90   11.566%   $219.6735   $219.67   $219.65   $219.70  
  Purchase #6 $109.88   5.299%   $115.7025   $115.70   $115.70   $115.70  
  Purchase #7 $38.95   10.606%   $43.081   $43.08   $43.10   $43.10  
  7 purchase totals = $967.30       $1,065.3098   $1,065.30   $1,065.30   $1,065.40