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 $87.90   8.714%   $95.5596   $95.56   $95.55   $95.60  
  Purchase #2 $6.69   10.828%   $7.4144   $7.41   $7.40   $7.40  
  Purchase #3 $142.28   6.329%   $151.2849   $151.28   $151.30   $151.30  
  Purchase #4 $193.88   9.693%   $212.6728   $212.67   $212.65   $212.70  
  Purchase #5 $164.91   7.773%   $177.7285   $177.73   $177.75   $177.70  
  Purchase #6 $54.36   11.553%   $60.6402   $60.64   $60.65   $60.60  
  Purchase #7 $98.39   13.346%   $111.5211   $111.52   $111.50   $111.50  
  7 purchase totals = $748.41       $816.8215   $816.81   $816.80   $816.80