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 $105.27   4.718%   $110.2366   $110.24   $110.25   $110.20  
  Purchase #2 $139.49   12.488%   $156.9095   $156.91   $156.90   $156.90  
  Purchase #3 $222.46   11.775%   $248.6547   $248.65   $248.65   $248.70  
  Purchase #4 $234.32   4.658%   $245.2346   $245.23   $245.25   $245.20  
  Purchase #5 $35.97   6.367%   $38.2602   $38.26   $38.25   $38.30  
  Purchase #6 $82.80   10.432%   $91.4377   $91.44   $91.45   $91.40  
  Purchase #7 $120.29   10.495%   $132.9144   $132.91   $132.90   $132.90  
  7 purchase totals = $940.60       $1,023.6477   $1,023.64   $1,023.65   $1,023.60